The Zig toolchain includes a zig.h header file that is included by header files generated using the -emit-h build flag. This change exposes that header file as a Bazel target that can be depended on by cc_* targets. It additionally sets the required CPP defines on the command-line.

• Add a rule to expose the builtin zig.h header
• Expose the builtin Zig header as Bazel target
• Test that zig.h can be included
• Update generated files
• Add unit test for max_int_alignment function
• Analysis test for ZIG_TARGET_MAX_INT_ALIGNMENT
• Multi-platform analysis test for zig.h defines