support CMake versions back to 3.0.2

Summary: Update CMakeLists.txt to support CMake versions as old as 3.0.2.

Reviewed By: yfeldblum

Differential Revision: D6843104

fbshipit-source-id: 43c2fc685c63df373ed33183f8144de779c97edf

CMake/FollyConfigChecks.cmake

@@ -116,7 +116,7 @@ if (NOT INT128_SIZE STREQUAL "")
     static_assert(
       ::std::is_same<::std::make_signed<unsigned __int128>::type,
                      __int128>::value,
-      \"signed form of \`unsigned __uint128\` must be \`__int128\`.\");
+      \"signed form of 'unsigned __uint128' must be '__int128'.\");
     int main() { return 0; }"
     HAVE_INT128_TRAITS
   )

CMakeLists.txt

-cmake_minimum_required(VERSION 3.2.0 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.0.2 FATAL_ERROR)
 # We use the GoogleTest module if it is available (only in CMake 3.9+)
-# It requires CMP0057 to be enabled.
+# It requires CMP0054 and CMP0057 to be enabled.
+if (POLICY CMP0054)
+  cmake_policy(SET CMP0054 NEW)
+endif()
 if (POLICY CMP0057)
   cmake_policy(SET CMP0057 NEW)
 endif()