Getting path to C/C++ standard library header directories

[mitchgrout]

A common problem when running custom lint jobs is being able to find where the language headers are stored. For example, I might have a basic file like

#include <stdio.h>
int main(void) { puts("Hello, world"); return 0; }

When running a linter against this (besides linters which integrate with a compiler toolchain such as clang-tidy), you might expect an error like

unable to open include file 'stdio.h'

The expected resolution is to pass the directory containing such libraries to the linter; however, meson has no way to deduce where these files are, just that they are present. We have things like compiler.check_header and compiler.find_library, could we also have something like compiler.system_includes() or similar for this purpose?

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Implementation-wise, for GCC and clang-like compilers, <compiler> -x <language> -E -Wp,-v empty-file would provide the include paths for <language>. The exact syntax for other compilers would likely be different, but surely could be extracted.