cmake: set compiler flags for non-Windows platforms

Summary:
Update CMakeLists.txt to check the current platform, and to set compiler flags
correctly.  It now uses flags for Microsoft Visual Studio on Windows, and flags
for gcc or clang on all other platforms.  Previously it unconditionally used
MSVC flags.

Reviewed By: meyering

Differential Revision: D6710435

fbshipit-source-id: dbae3097bcadf1ee4a25879dd7770603387c0e4d

CMake/FollyCompilerUnix.cmake

+set(CMAKE_CXX_FLAGS_COMMON -g -Wall -Wextra)
+set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_COMMON}")
+set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_COMMON} -O3")
+
+function(apply_folly_compile_options_to_target THETARGET)
+  target_compile_options(${THETARGET}
+    PUBLIC
+      -g
+      -std=gnu++14
+      -fopenmp
+      -finput-charset=UTF-8
+      -fsigned-char
+      -faligned-new
+      -Werror
+      -Wall
+      -Wno-deprecated
+      -Wdeprecated-declarations
+      -Wno-error=deprecated-declarations
+      -Wno-sign-compare
+      -Wno-unused
+      -Wunused-label
+      -Wunused-result
+      -Wnon-virtual-dtor
+      -Wno-noexcept-type
+    PRIVATE
+      -D_REENTRANT
+      -D_GNU_SOURCE
+  )
+endfunction()

CMakeLists.txt

@@ -86,7 +86,11 @@ configure_file(
   ${CMAKE_CURRENT_BINARY_DIR}/folly/folly-config.h
 )
 
-include(FollyCompiler)
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
+  include(FollyCompilerMSVC)
+else()
+  include(FollyCompilerUnix)
+endif()
 include(FollyFunctions)
 
 # Main folly library files
@@ -196,11 +200,21 @@ else()
 endif()
 
 
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
+  set(FOLLY_LINK_LIBRARIES
+    ${FOLLY_LINK_LIBRARIES}
+    Iphlpapi.lib
+    Ws2_32.lib
+  )
+else()
+  set(FOLLY_LINK_LIBRARIES
+    ${FOLLY_LINK_LIBRARIES}
+    dl
+  )
+endif()
+
 set(FOLLY_LINK_LIBRARIES
   ${FOLLY_LINK_LIBRARIES}
-  Iphlpapi.lib
-  Ws2_32.lib
-
   ${FOLLY_SHINY_DEPENDENCIES}
 )