Alter FailFast behaviour of memcpy (#526)

This commit changes the codegen for error messages for failed memcpys.
This no longer generates a stack frame and correctly tail calls the
error messages generator.

It also turns the error messages on in Release builds.  This will lead
to better adoption experience.

src/test/perf/memcpy/memcpy.cc

@@ -90,7 +90,12 @@ void memcpy_unchecked(void* dst, const void* src, size_t size)
 NOINLINE
 void memcpy_platform_checked(void* dst, const void* src, size_t size)
 {
-  check_bounds(dst, size, "");
+  if (SNMALLOC_UNLIKELY(!check_bounds(dst, size)))
+  {
+    report_fatal_bounds_error(dst, size, "");
+    return;
+  }
+
   memcpy(dst, src, size);
 }