use zig as a c compiler

[andrewrk]

zig cc foo.c

All args after cc are args exactly as you would pass to clang. We depend on libclang, might as well expose it.

In the std build API, the default way to compile C code would be with this, instead of with an external compiler. Using an external compiler is still useful and supported, however.

Being a C++ compiler is a little tricker, since we would need to know the location of libstdc++ in addition to libc, and all the weird versioning stuff that goes along with it.

[PavelVozenilek]

There should be some macro identifying that it is "zig compiler" and its version.

[andrewrk]

Sure, we can do:

#define __zig__ 1
#define __zig_version__ "0.0.0"
#define __zig_major__ 0
#define __zig_minor__ 0
#define __zig_patchlevel__ 0

to match clang. The corresponding clang defines will still exist.