Align Kconfig and Kbuild logic to Linux 4.20 release with minimal impact
on files outside of this scope.

Our previous Kconfig sync was done by commit 587e4a42 ("kconfig /
kbuild: Re-sync with Linux 4.19").

As part of this re-sync, a few related changes from previous Linux
releases were found to have been missed and merged in, and are not in
the following list.

The imported Linux commits are:

[From prior to v4.19]
b1e0d8b70fa3 kbuild: Fix gcc -x syntax
a4353898980c kconfig: add CC_IS_GCC and GCC_VERSION
469cb7376c06 kconfig: add CC_IS_CLANG and CLANG_VERSION

[From v4.19 to v4.20]
487c7c7702ab kbuild: prefix Makefile.dtbinst path with $(srctree) unconditionally
0d91bf584fe5 kbuild: remove old check for CFLAGS use
25815cf5ffec kbuild: hide most of targets when running config or mixed targets
00d78ab2ba75 kbuild: remove dead code in cmd_files calculation in top Makefile
23066c3f4e21 Compiler Attributes: enable -Wstringop-truncation on W=1 (gcc >= 8)
37c8a5fafa3b kbuild: consolidate Devicetree dtb build rules
80463f1b7bf9 kbuild: add --include-dir flag only for out-of-tree build
77ec0c20c7e0 kbuild: remove VERSION and PATCHLEVEL from $(objtree)/Makefile
74bc0c09b2da kbuild: remove user ID check in scripts/mkmakefile
4fd61277f662 kbuild: do not pass $(objtree) to scripts/mkmakefile
80d0dda3a4e5 kbuild: simplify command line creation in scripts/mkmakefile
fb073a4b473e kbuild: add -Wno-pointer-sign flag unconditionally
9df3e7a7d7d6 kbuild: add -Wno-unused-but-set-variable flag unconditionally
69ea912fda74 kbuild: remove unneeded link_multi_deps
7d0ea2524202 kbuild: use 'else ifeq' for checksrc to improve readability
04c459d20448 kconfig: remove oldnoconfig target
0085b4191f3e kconfig: remove silentoldconfig target
3f80babd9ca4 kbuild: remove unused cc-fullversion variable
2cd3faf87d2d merge_config.sh: Allow to define config prefix
076f421da5d4 kbuild: replace cc-name test with CONFIG_CC_IS_CLANG
6bbe4385d035 kconfig: merge_config: avoid false positive matches from comment lines

[From post v4.20]
885480b08469 Makefile: Move -Wno-unused-but-set-variable out of GCC only block

There are a number of changes related to additional warnings as well as
being able to drop cc-name entirely that have been omitted for now as
additional work is required first.

Cc: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: NTom Rini <trini@konsulko.com>

The way that we have been handling additional DTC warning flags hasn't
matched the way the Linux Kernel does.  Resync this logic with v4.17.
Signed-off-by: NTom Rini <trini@konsulko.com>

While our "extrawarns" logic has gotten out of sync with upstream
Kbuild, for now lets start by bringing in the latest set of DTC_FLAGS
from the Linux Kernel 5.0 to match their behavior in silencing warnings
from dtc.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: NTom Rini <trini@konsulko.com>

When U-Boot started using SPDX tags we were among the early adopters and
there weren't a lot of other examples to borrow from.  So we picked the
area of the file that usually had a full license text and replaced it
with an appropriate SPDX-License-Identifier: entry.  Since then, the
Linux Kernel has adopted SPDX tags and they place it as the very first
line in a file (except where shebangs are used, then it's second line)
and with slightly different comment styles than us.

In part due to community overlap, in part due to better tag visibility
and in part for other minor reasons, switch over to that style.

This commit changes all instances where we have a single declared
license in the tag as both the before and after are identical in tag
contents.  There's also a few places where I found we did not have a tag
and have introduced one.
Signed-off-by: NTom Rini <trini@konsulko.com>

Using the update-dtc-source.sh script from Linux v4.14-rc1 import the
portions of dtc that we require.  We bring in update-dtc-source.sh and
scripts/dtc/Makefile from Linux v4.14-rc1.  Rework DTC_FLAGS handling to
not require a test.
Signed-off-by: NTom Rini <trini@konsulko.com>

Recent commits of DTC introduced new warnings checking PCI and simple
buses, unit address formatting, and stricter node and property name
checking.  Disable the new DTC warnings by default.  As before,
warnings are enabled with W=*.  The strict node and property name
checks are a bit subjective, so they are only enabled for W=2.
(This policy reflects the commit 8654cb8d0371 of Linux.)
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

DTC 1.4.2 or later checks DT unit-address without reg property and
vice-versa, and generates lots of warnings.  Fixing DT files will
take for a while.  Until then, let's turn off the check unless
building with W=*.

Introduce a new helper dtc-option to check if the option is supported
in order to suppress warnings on older versions.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: NSimon Glass <sjg@chromium.org>
Tested-by: NBin Meng <bmeng.cn@gmail.com>

A general best practice for SPDX is that Makefiles should have an
identifier, add these as everything else is currently covered.
Signed-off-by: NTom Rini <trini@konsulko.com>

These lines originate in Linux;  it looks like Linux folks chose to
hide bunch of warnings reported by clang rather than fixing C code.

In U-boot, warnings are being fixed thanks to Jeroen's great efforts.
Let's stop suppressing clang warnings.
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Jeroen Hofstee <jeroen@myspectrum.nl>

This commit was imported from Linux Kernel:
commit a86fe353 written by me.

W=... provides extra gcc checks.

Having such code in scripts/Makefile.build results in the same flags
being added to KBUILD_CFLAGS multiple times becuase
scripts/Makefile.build is invoked every time Kbuild descends into
the subdirectories.

Since the top Makefile is already too cluttered, this commit moves
all of extra gcc check stuff to a new file scripts/Makefile.extrawarn,
which is included from the top Makefile.
Signed-off-by: NMasahiro Yamada <yamada.m@jp.panasonic.com>