Re-vendor, and use mtrmac/image-spec:id-based-loader to fix tests

Anyone running (vndr) currently ends up with failing tests in OCI schema
validation because gojsonschema has fixed its "$ref" interpretation, exposing
inconsistent URI usage inside image-spec/schema.

So, this runs (vndr), and uses mtrmac/image-spec:id-based-loader
( https://github.com/opencontainers/image-spec/pull/739 ) to make the tests pass
again.  As soon as that PR is merged we should revert to using the upstream
image-spec repo again.

vendor/golang.org/x/sys/unix/gccgo.go

@@ -11,9 +11,19 @@ import "syscall"
 // We can't use the gc-syntax .s files for gccgo. On the plus side
 // much of the functionality can be written directly in Go.
 
+//extern gccgoRealSyscallNoError
+func realSyscallNoError(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r uintptr)
+
 //extern gccgoRealSyscall
 func realSyscall(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r, errno uintptr)
 
+func SyscallNoError(trap, a1, a2, a3 uintptr) (r1, r2 uintptr) {
+	syscall.Entersyscall()
+	r := realSyscallNoError(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	syscall.Exitsyscall()
+	return r, 0
+}
+
 func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
 	syscall.Entersyscall()
 	r, errno := realSyscall(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
@@ -35,6 +45,11 @@ func Syscall9(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr,
 	return r, 0, syscall.Errno(errno)
 }
 
+func RawSyscallNoError(trap, a1, a2, a3 uintptr) (r1, r2 uintptr) {
+	r := realSyscallNoError(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
+	return r, 0
+}
+
 func RawSyscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err syscall.Errno) {
 	r, errno := realSyscall(trap, a1, a2, a3, 0, 0, 0, 0, 0, 0)
 	return r, 0, syscall.Errno(errno)