all: Become a Go module (fixes #5148) (#5384)

* go mod init; rm -rf vendor

* tweak proto files and generation

* go mod vendor

* clean up build.go

* protobuf literals in tests

* downgrade gogo/protobuf

vendor/golang.org/x/sys/unix/gccgo_c.c

@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build gccgo
+// +build !aix
 
 #include <errno.h>
 #include <stdint.h>
@@ -31,11 +32,8 @@ gccgoRealSyscall(uintptr_t trap, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintp
 	return r;
 }
 
-// Define the use function in C so that it is not inlined.
-
-extern void use(void *) __asm__ (GOSYM_PREFIX GOPKGPATH ".use") __attribute__((noinline));
-
-void
-use(void *p __attribute__ ((unused)))
+uintptr_t
+gccgoRealSyscallNoError(uintptr_t trap, uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4, uintptr_t a5, uintptr_t a6, uintptr_t a7, uintptr_t a8, uintptr_t a9)
 {
+	return syscall(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9);
 }