(this will be needed for snapshotting at some point).

Came back to look at rust and found out that this had been broken by some refactoring work. Fixed and now has tests.

r? @thestinger 

Fixes #5341

The chunk fix is cherry picked from @graydon's `gc` branch.

Continuation of #5317. Actually use operands properly now, including any number of output operands.

Which means you can do things like call printf:
```Rust
fn main() {
    unsafe {
        do str::as_c_str(~"The answer is %d.\n") |c| {
            let a = 42;
            asm!("mov $0, %rdi\n\t\
                  mov $1, %rsi\n\t\
                  xorl %eax, %eax\n\t\
                  call _printf"
                 :
                 : "r"(c), "r"(a)
                 : "rdi", "rsi", "eax"
                 : "volatile","alignstack"
                 );
        }
    }
}
```

```
% rustc foo.rs
% ./foo
The answer is 42.
```

Or just add 2 numbers:
```Rust
fn add(a: int, b: int) -> int {
    let mut c = 0;
    unsafe {
        asm!("add $2, $0"
             : "=r"(c)
             : "0"(a), "r"(b)
             );
    }
    c
}

fn main() {
    io::println(fmt!("%d", add(1, 2)));
}
```

```
% rustc foo.rs
% ./foo
3
```

Multiple outputs!
```Rust
fn addsub(a: int, b: int) -> (int, int) {
    let mut c = 0;
    let mut d = 0;
    unsafe {
        asm!("add $4, $0\n\t\
              sub $4, $1"
             : "=r"(c), "=r"(d)
             : "0"(a), "1"(a), "r"(b)
             );
    }
    (c, d)
}

fn main() {
    io::println(fmt!("%?", addsub(5, 1)));
}
```
```
% rustc foo.rs
% ./foo
(6, 4)
```

This also classifies inline asm as RvalueStmtExpr instead of the somewhat arbitrary kind I made it initially. There are a few XXX's regarding what to do in the liveness and move passes.

Also turn `copy` into `.clone()` in much of run-pass.

Add a conditional compile option for android

r?

I want to use this function as a method. There's probably a better way to design this but the existing `ToBytes` trait is not what I am looking for (it has a parameter to indicate the byte order).

r? @nikomatsakis 
r? @erickt 

Before this change, encoding an object containing a codemap::span
using the JSON encodeng produced invalid JSON, for instance:
[{"span":,"global":false,"idents":["abc"]}]
Since the decoder for codemap::span's ignores its argument, I
conjecture that this will not damage decoding, and should improve
it for many decoders.

LLVM could not recognize target-os when target-triple was given as like 'arm-linux-androideabi'.
Normalizing target-triple fill the missing elements. 
In the case of 'arm-linux-androideabi', nomalized target-triple will be "arm-unknown-linux-androideabi" and this let llvm recognize the triple correctly. (arch: arm, vendor: unknown, os: linux, environment: android)

Before this change, encoding an object containing a codemap::span
using the JSON encodeng produced invalid JSON, for instance:
[{"span":,"global":false,"idents":["abc"]}]
Since the decoder for codemap::span's ignores its argument, I
conjecture that this will not damage decoding, and should improve
it for many decoders.