files.  The first two, 6g.go and 6c.c, are a Go source file for 6g and
a C source file for 6c; both compile as part of the named package
(gmp, in this example).  The third, gcc.c, is a C source file for gcc;
it compiles into a shared object (.so) that is dynamically linked into
any 6.out that imports the first two files.

The stanza

	// #include <gmp.h>
	import "C"

is a signal to cgo.  The doc comment on the import of "C" provides

pkg syscall (freebsd-386-cgo), const MAP_RENAME ideal-int
pkg syscall (freebsd-386-cgo), const MAP_RESERVED0080 ideal-int
pkg syscall (freebsd-386-cgo), const MAP_RESERVED0100 ideal-int
pkg syscall (freebsd-386-cgo), const MAP_SHARED ideal-int
pkg syscall (freebsd-386-cgo), const MAP_STACK ideal-int
pkg syscall (freebsd-386-cgo), const MCL_CURRENT ideal-int
pkg syscall (freebsd-386-cgo), const MCL_FUTURE ideal-int