parsing these is significantly less work and more robust than parsing
C source.

Cgo first invokes gcc -E -dM on the preamble, in order to find out
about simple #defines for constants and the like. These are recorded
for later use.

Next, cgo needs to identify the kinds for each identifier. For the
identifiers C.foo, cgo generates this C program:

	<preamble>
	#line 1 "not-declared"

		Set expected package import to pkgpath.
	-shared
		Generate code that can be linked into a shared library.
	-spectre list
		Enable spectre mitigations in list (all, ret).
	-trimpath prefix
		Remove prefix from recorded source file paths.
	-v
		Print debug output.

Input language:

The assembler uses mostly the same syntax for all architectures,
the main variation having to do with addressing modes. Input is