Remove -s compile option from release mode (#3367)

Summary:
This compile option causes a lot of warnings in cmake build:

```
clang: warning: argument unused during compilation: '-s' [-Wunused-command-line-argument]
```

So removing it for now.

Pull Request resolved: #3367

Reviewed By: dbort

Differential Revision: D56617190

Pulled By: larryliu0820

fbshipit-source-id: 950a122b55deb5d5d3c15d0e46745b6697c8f7ba

Author: larryliu0820

CMakeLists.txt

@@ -120,7 +120,7 @@ endif()
 # disables exceptions and runtime type.
 set(CMAKE_CXX_FLAGS_RELEASE
     "-ffunction-sections -fdata-sections -fno-exceptions -fno-rtti")
-if(NOT APPLE)
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
   set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -s")
 endif()