clang on mac doesn't seem to want -pthread

compiler.cmake

@@ -1,10 +1,10 @@
 include(CheckCXXCompilerFlag)
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wpointer-arith -Wnon-virtual-dtor -Wshadow -Wformat -pthread")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wpointer-arith -Wnon-virtual-dtor -Wshadow -Wformat")
 if (NOT RCT_RTTI_ENABLED)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
 endif ()
 
-set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wpointer-arith -Wshadow -Wformat -pthread")
+set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wpointer-arith -Wshadow -Wformat") # -pthread")
 if (CMAKE_SYSTEM_NAME MATCHES "CYGWIN")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu11")
@@ -17,6 +17,8 @@ if (CMAKE_SYSTEM_NAME MATCHES "Darwin")
   add_definitions(-D_DARWIN_UNLIMITED_SELECT)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libc++")
 else ()
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -pthread")
   if (NOT CMAKE_SYSTEM_NAME MATCHES "CYGWIN")
     # Use pic instead of PIC, which produces faster and smaller code,
     # but could eventully lead to linker problems.