enable -Werror based on compiler version

older gcc's (e.g gcc4.8) have issues with some const expressions
so they print warnings. we don't want to change the code because it is
fine with newer compilers. therefore we only enable -Werror for
newer versions of gcc

CMakeLists.txt

@@ -275,7 +275,7 @@ macro(ADD_CXX_COMPILER_FLAG_IF_AVAILABLE flag have)
 endmacro(ADD_CXX_COMPILER_FLAG_IF_AVAILABLE)
 
 if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -Wno-comment -Wno-reorder -Wno-unused-but-set-variable -Wno-unused-variable -Wtype-limits -std=c++11")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wno-comment -Wno-reorder -Wno-unused-but-set-variable -Wno-unused-variable -Wtype-limits -std=c++11")
 
   find_package(SSE)
   if (HAVE_AVX2)
@@ -292,7 +292,7 @@ endif(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clan
 ADD_CXX_COMPILER_FLAG_IF_AVAILABLE("-Werror=incompatible-pointer-types" HAVE_ERROR_INCOMPATIBLE)
 
 if(CMAKE_C_COMPILER_ID MATCHES "GNU" OR CMAKE_C_COMPILER_ID MATCHES "Clang")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Werror -Wno-comment -Wno-write-strings -Winline -Wno-unused-result -Wformat -Wmissing-field-initializers -Wtype-limits -std=c99 -D_GNU_SOURCE")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wno-comment -Wno-write-strings -Winline -Wno-unused-result -Wformat -Wmissing-field-initializers -Wtype-limits -std=c99 -D_GNU_SOURCE")
 
   if(${CMAKE_BUILD_TYPE} STREQUAL "Debug")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -ggdb -O0 -DDEBUG_MODE -DBUILD_TYPE_DEBUG")
@@ -382,6 +382,13 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
    set(CMAKE_SHARED_LINKER_FLAGS "-undefined dynamic_lookup")
 endif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
 
+
+# Add -Werror to C/C++ flags for newer compilers
+if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9)
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror")
+endif()
+
 message(STATUS "CMAKE_C_FLAGS is ${CMAKE_C_FLAGS}")
 message(STATUS "CMAKE_CXX_FLAGS is ${CMAKE_CXX_FLAGS}")