Current `-Zinstrument-mcount` for ARM32 use the `\01__gnu_mcount_nc`
directly for its instrumentation function.

However, the LLVM does not use this mcount function directly, but it wraps
it to intrinsic, `llvm.arm.gnu.eabi.mcount` and the transform pass also
only handle the intrinsic.

As a result, current `-Zinstrument-mcount` not work on ARM32.
Refer: https://github.com/namhyung/uftrace/issues/1764

This commit replaces the mcount name from native function to the
LLVM intrinsic so that the transform pass can handle it.
Signed-off-by: NChoKyuWon <kyuwoncho18@gmail.com>

All eabi targets have target_abi = "eabi".
All eabihf targets have target_abi = "eabihf".
armv6_unknown_freebsd and armv7_unknown_freebsd have target_abi = "eabihf".
All abi64 targets have target_abi = "abi64".
All ilp32 targets have target_abi = "ilp32".
All softfloat targets have target_abi = "softfloat".
All *-uwp-windows-* targets have target_abi = "uwp".
All spe targets have target_abi = "spe".
All macabi targets have target_abi = "macabi".
aarch64-apple-ios-sim has target_abi = "sim".
x86_64-fortanix-unknown-sgx has target_abi = "fortanix".
x86_64-unknown-linux-gnux32 has target_abi = "x32".

Add FIXME entries for targets for which existing values need to change
once cfg_target_abi becomes stable. (All of them are tier 3 targets.)

Add a test for target_abi in `--print cfg`.

It makes very little sense to maintain denylists of ABIs when, as far as
non-generic ABIs are concerned, targets usually only support a small
subset of the available ABIs.

This has historically been a cause of bugs such as us allowing use of
the platform-specific ABIs on x86 targets – these in turn would cause
LLVM errors or assertions to fire.

Fixes #57182

Sponsored by: standard.ai

`target.target_endian` -> `target.endian`
`target.target_c_int_width` -> `target.c_int_width`
`target.target_os` -> `target.os`
`target.target_env` -> `target.env`
`target.target_vendor` -> `target.vendor`
`target.target_family` -> `target.os_family`
`target.target_mcount` -> `target.mcount`

Also change target_pointer_width to pointer_width.

Preparation for a subsequent type change of
target_pointer_width to an integer together with a rename
to pointer_width.

On its own, this commit breaks the build. I don't like making
build-breaking commits, but in this instance I believe that it
makes review easier, as the "real" changes of this PR can be
seen much more easily.

Result of running:

find compiler/rustc_target/src/spec/ -type f -exec sed -i -e 's/target_pointer_width: "\(.*\)"\..*,/pointer_width: \1,/g' {} \;

Construction of a built-in target is always infallible now, so `TargetResult` is no longer necessary.

Other terms are more inclusive and precise.

Clippy still has a lint named "blacklisted-name", but renaming it would
be a breaking change, so is left for future work.

The target configuration option "abi-blacklist" has been depreciated and
renamed to "unsupported-abis". The old name continues to work.

As discovered in #44538 ARMv6 devices may or may not support unaligned memory accesses. ARMv6
Linux *seems* to have no problem with unaligned accesses but this is because the kernel is stepping
in to fix each unaligned memory access -- this incurs in a performance penalty.

This commit enforces aligned memory accesses on all our in-tree ARM targets that may be used with
ARMv6 devices. This should improve performance of Rust programs on ARMv6 devices. For the record,
clang also applies this attribute when targeting ARMv6 devices that are not running Darwin or
NetBSD.

(all i32 for now, as in liblibc)

This patch adds a `-Z linker-flavor` flag to rustc which can be used to invoke
the linker using a different interface.

For example, by default rustc assumes that all the Linux targets will be linked
using GCC. This makes it impossible to use LLD as a linker using just `-C
linker=ld.lld` because that will invoke LLD with invalid command line
arguments. (e.g. rustc will pass -Wl,--gc-sections to LLD but LLD doesn't
understand that; --gc-sections would be the right argument)

With this patch one can pass `-Z linker-flavor=ld` to rustc to invoke the linker
using a LD-like interface. This way, `rustc -C linker=ld.lld -Z
linker-flavor=ld` will invoke LLD with the right arguments.

`-Z linker-flavor` accepts 4 different arguments: `em` (emcc), `ld`,
`gcc`, `msvc` (link.exe). `em`, `gnu` and `msvc` cover all the existing linker
interfaces. `ld` is a new flavor for interfacing GNU's ld and LLD.

This patch also changes target specifications. `linker-flavor` is now a
mandatory field that specifies the *default* linker flavor that the target will
use. This change also makes the linker interface *explicit*; before, it used to
be derived from other fields like linker-is-gnu, is-like-msvc,
is-like-emscripten, etc.

Another change to target specifications is that the fields `pre-link-args`,
`post-link-args` and `late-link-args` now expect a map from flavor to linker
arguments.

``` diff
-    "pre-link-args": ["-Wl,--as-needed", "-Wl,-z,-noexecstack"],
+    "pre-link-args": {
+        "gcc": ["-Wl,--as-needed", "-Wl,-z,-noexecstack"],
+        "ld": ["--as-needed", "-z,-noexecstack"],
+    },
```

[breaking-change]  for users of custom targets specifications

to better express the idea that omitting this field defaults this value
to target_pointer_width

Change all the target generation functions to return a Result<Target,
String> so that targets that are unable to be instantiated can be
expressed as an Err instead of a panic!(). This should improve #33497 as
well.

Right now they're `gnueabihf` and `gnueabi`, but when adding new platforms like
musl on ARM it's unfortunate to have to test for all three (`musl`, `musleabi`,
and `musleabihf`). This PR switches everything currently to `gnu`, and the new
musl targets can also use `musl` when they land.

Closes #33244

This adds a new target property, `target_vendor` which can be used as a
matcher for conditional compilation. The vendor is part of the autoconf
target triple: <arch><sub>-<vendor>-<os>-<env>

The default value for `target_vendor` is "unknown".

Matching against the `target_vendor` with `#[cfg]` is currently feature
gated as `cfg_target_vendor`.

Turns out for OSX our data layout was subtly wrong and the LLVM update must have
exposed this. Instead of fixing this I've removed all data layouts from the
compiler to just use the defaults that LLVM provides for all targets. All data
layouts (and a number of dead modules) are removed from the compiler here.
Custom target specifications can still provide a custom data layout, but it is
now an optional key as the default will be used if one isn't specified.

This adds a new `#[cfg]` matcher against the `target_env` property of the
destination target triple. For example all windows triples today end with `-gnu`
but we will also hopefully support non-`gnu` targets for Windows, at which point
we'll need to differentiate between the two. This new `target_env` matches is
provided and filled in with the target's environment name.

Currently the only non-empty value of this name is `gnu`, but `musl` will be
shortly added for the linux triples.

Closes #20421

[breaking-change]

According to http://llvm.org/docs/LangRef.html#data-layout correct syntax
for data layout is `a:<abi>:<pref>` so it looks like  `a0:<abi>:<pref>` is
either a typo or outdated syntax (as it goes back pretty deep in time)