Redefine FBGEMM targets with gpu_cpp_library [25/N] (pytorch#3217)

Summary:
Pull Request resolved: pytorch#3217

X-link: facebookresearch/FBGEMM#314

- Add `default_compiler_flags` to codegen targets

- Fix inclusion of `feature_gates_fb.h`

Reviewed By: jianyuh

Differential Revision: D63818462

fbshipit-source-id: d73fcc69e4f72291793daf22b5faa04467b3c8af

fbgemm_gpu/include/fbgemm_gpu/config/feature_gates.h

@@ -11,7 +11,7 @@
 #include <string>
 
 #ifdef FBGEMM_FBCODE
-#include "fbgemm_gpu/config/feature_gates_fb.h"
+#include "deeplearning/fbgemm/fbgemm_gpu/fb/include/fbgemm_gpu/config/feature_gates_fb.h"
 #endif
 
 /// @defgroup fbgemm-gpu-config FBGEMM_GPU Configuration