Basic go_library functionality

empty

Checks that a go_library will compile and link even if all the sources (including assembly sources) are filtered out by build constraints.

asm_include

Checks that assembly files in a go_library may include other assembly files in the same library. Verifies `#1520`_.

asm_header

Checks that assembly files in a go_library may include "go_asm.h", generated by the compiler. Verifies `#1262`_.