SWDEV-323669 - Improve arch detection

- Clean up detection by using visual studio macros to detect arch; I
  didn't list all possible ARM platforms (can be done later if desired)
- Fixed two incorrect uses of !defined(ATI_ARCH_ARM) to instead use
  defined(ATI_ARCH_X86), as they contain X86 specific code
- Fixed one use of __ARM_ARCH_7A__ to use ATI_ARCH_ARM instead

This is an improvement to the fixes in the last patch for SWDEV-323669

Signed-off-by: Jeremy Newton <Jeremy.Newton@amd.com>
Change-Id: I8568167293c34ad5331902105877f3ab6e25acb3

rocclr/os/os_posix.cpp

@@ -701,14 +701,14 @@ void Os::setCurrentStackPtr(address sp) {
   sp -= sizeof(void*);
   *(void**)sp = __builtin_return_address(0);
 
-#if defined(ATI_ARCH_ARM)
-  assert(!"Unimplemented");
-#else
+#if defined(ATI_ARCH_X86)
   __asm__ __volatile__(
 #if !defined(OMIT_FRAME_POINTER)
       LP64_SWITCH("movl (%%ebp),%%ebp;", "movq (%%rbp),%%rbp;")
 #endif  // !OMIT_FRAME_POINTER
           LP64_SWITCH("movl %0,%%esp; ret;", "movq %0,%%rsp; ret;")::"r"(sp));
+#else
+  assert(!"Unimplemented");
 #endif
 }