Zig supports various C source type inputs. For each each such input it tracks the most recent set of -cflags ... -- surround C flags. The C files are compiled to objects using llvm and linked into the final output. Fortunately, we don't need to worry about link-order, because the Zig linker takes care of resolving dependencies either way.

• end-to-end test
• handle csrcs and copts
• unit-test for copts (surrounded by -cflags ... --, if set, omitted otherwise)
• unit-test for csrcs (all included on command-line)