[MSan] Implement _nosanitize functions in compiler-rt

[glider]

Summary

This is a follow-up for https://reviews.llvm.org/D56171 that implements _nosanitize versions of memory intrinsic functions.

[eugenis]

Please add a test.

[glider]

Added a test.

[eugenis]

On a second thought, this is wrong. Unsanitized (blacklisted) functions are supposed to unpoison anything they touch. The new _nosanitize variants must unpoison their target memory.

lib/msan/msan_interceptors.cc

if (msan_init_is_running || __msan::IsInSymbolizer())
     return REAL(memcpy)(dest, src, n);
   ENSURE_MSAN_INITED();
   GET_STORE_STACK_TRACE;
   void *res = REAL(memcpy)(dest, src, n);
   CopyShadowAndOrigin(dest, src, n, &stack);
   return res;
 }
 
+void *__msan_memcpy_nosanitize(void *dest, const void *src, SIZE_T n) {
+  if (!msan_inited) return internal_memcpy(dest, src, n);
+  return REAL(memcpy)(dest, src, n);
+}
+
 void *__msan_memset(void *s, int c, SIZE_T n) {
   if (!msan_inited) return internal_memset(s, c, n);
   if (msan_init_is_running) return REAL(memset)(s, c, n);
   ENSURE_MSAN_INITED();
   void *res = REAL(memset)(s, c, n);
   __msan_unpoison(s, n);
   return res;
 }
 
+void *__msan_memset_nosanitize(void *s, int c, SIZE_T n) {
+  if (!msan_inited) return internal_memset(s, c, n);
+  return REAL(memset)(s, c, n);
+}
+
 void *__msan_memmove(void *dest, const void *src, SIZE_T n) {
   if (!msan_inited) return internal_memmove(dest, src, n);
   if (msan_init_is_running) return REAL(memmove)(dest, src, n);
   ENSURE_MSAN_INITED();
   GET_STORE_STACK_TRACE;
   void *res = REAL(memmove)(dest, src, n);
   MoveShadowAndOrigin(dest, src, n, &stack);
   return res;
 }
 
+void *__msan_memmove_nosanitize(void *dest, const void *src, SIZE_T n) {
+  if (!msan_inited) return internal_memmove(dest, src, n);
+  return REAL(memmove)(dest, src, n);
+}
+
 void __msan_unpoison_string(const char* s) {
   if (!MEM_IS_APP(s)) return;
   __msan_unpoison(s, REAL(strlen)(s) + 1);
 }
 
 namespace __msan {
 
 void InitializeInterceptors() {