tools: Add tool for checking size and alignment of C types

[ehaas]

Requested by @alexrp

Prints _Static_asserts for the size and alignment of all the basic built-in C types.

The output can be run through a compiler for the specified target to verify that Zig's values are the same as those used by a C compiler for the target.

Example output for x86_64-linux-gnu:

_Static_assert(sizeof(char) == 1, "");
_Static_assert(_Alignof(char) == 1, "");

_Static_assert(sizeof(short) == 2, "");
_Static_assert(_Alignof(short) == 2, "");

_Static_assert(sizeof(unsigned short) == 2, "");
_Static_assert(_Alignof(unsigned short) == 2, "");

_Static_assert(sizeof(int) == 4, "");
_Static_assert(_Alignof(int) == 4, "");

_Static_assert(sizeof(unsigned int) == 4, "");
_Static_assert(_Alignof(unsigned int) == 4, "");

_Static_assert(sizeof(long) == 8, "");
_Static_assert(_Alignof(long) == 8, "");

_Static_assert(sizeof(unsigned long) == 8, "");
_Static_assert(_Alignof(unsigned long) == 8, "");

_Static_assert(sizeof(long long) == 8, "");
_Static_assert(_Alignof(long long) == 8, "");

_Static_assert(sizeof(unsigned long long) == 8, "");
_Static_assert(_Alignof(unsigned long long) == 8, "");

_Static_assert(sizeof(float) == 4, "");
_Static_assert(_Alignof(float) == 4, "");

_Static_assert(sizeof(double) == 8, "");
_Static_assert(_Alignof(double) == 8, "");

_Static_assert(sizeof(long double) == 16, "");
_Static_assert(_Alignof(long double) == 16, "");

[alexrp]

Already finding bugs:

❯ zig run generate_c_size_and_align_checks.zig -- sparc64-linux-gnu | sparc64-linux-gnu-gcc -fsyntax-only -xc -
<stdin>:35:1: error: static assertion failed: "_Alignof(long double) == 8"

[alexrp]

Another nice addition here would be to test __alignof(T) == target.c_type_preferred_alignment(c_type).

[andrewrk]

Thanks!

[nektro]

a nice followup enhancement would be adding a test step that creates run steps with the output of this program for a matrix of targets that we support