[NFC][AMDGPU] Require x86-registered-target for llvm/test/Transforms/MemCpyOpt/no-libcalls.ll

The test sets `-mtriple=x86_64` but doesn't require it. This can cause issue on
non-x86 system.

Author: shiltian

llvm/test/Transforms/MemCpyOpt/no-libcalls.ll

@@ -5,6 +5,7 @@
 ; RUN:     | FileCheck %s --check-prefixes=CHECK,LIBCALLS
 
 ; REQUIRES: amdgpu-registered-target
+; REQUIRES: x86-registered-target
 
 define void @dont_create_memset(ptr %p) {
 ; LIBCALLS-LABEL: @dont_create_memset(