[asan] Enable memtrinsics interception for RTEMS

[waltl]

Summary

Replace decltype(memcpy) with decltype(__asan_memcpy) because memcpy
has not been defined in any headers on RTEMS. Similarly for memmove
and memset.

lib/asan/asan_interceptors_memintrinsics.cc

 void *__asan_memset(void *block, int c, uptr size) {
   ASAN_MEMSET_IMPL(nullptr, block, c, size);
 }
 
 void *__asan_memmove(void *to, const void *from, uptr size) {
   ASAN_MEMMOVE_IMPL(nullptr, to, from, size);
 }
 
-#if SANITIZER_FUCHSIA
+#if SANITIZER_FUCHSIA || SANITIZER_RTEMS
 
 // Fuchsia doesn't use sanitizer_common_interceptors.inc, but the only
 // things there it wants are these three.  Just define them as aliases
 // here rather than repeating the contents.
 
-decltype(memcpy) memcpy[[gnu::alias("__asan_memcpy")]];
-decltype(memmove) memmove[[gnu::alias("__asan_memmove")]];
-decltype(memset) memset[[gnu::alias("__asan_memset")]];
+decltype(__asan_memcpy) memcpy[[gnu::alias("__asan_memcpy")]];
+decltype(__asan_memmove) memmove[[gnu::alias("__asan_memmove")]];
+decltype(__asan_memset) memset[[gnu::alias("__asan_memset")]];
 
-#endif  // SANITIZER_FUCHSIA
+#endif  // SANITIZER_FUCHSIA || SANITIZER_RTEMS