Add warning about old gcc when !HAVE_WORKING_REGEX

Related to ee859d8.

CMakeLists.txt

@@ -90,7 +90,7 @@ REQUIRE_CXX_SOURCE_COMPILES("template<class... T> class C; int main() { return 0
 # implementation for some things (like std::regex_iterator).
 # This needs to test *linking*, not compilation; cmake does both at the same
 # time, so the test below works.
-REQUIRE_CXX_SOURCE_COMPILES("#include <regex>\nint main() { std::cregex_iterator ri; }" HAVE_WORKING_REGEX)
+REQUIRE_CXX_SOURCE_COMPILES("#include <regex>\nint main() { std::cregex_iterator ri; }" HAVE_WORKING_REGEX " If you are using gcc, please update to gcc 4.9.")
 
 if(MSVC_VERSION GREATER 1499)
 		list(APPEND OC_CXX_FLAGS /MP)

README

@@ -41,6 +41,7 @@ system. For Debian based distributions, you will need these packages:
   libglew-dev libgtk2.0-dev libjpeg-dev libpng-dev libsdl1.2-dev
   libsdl-mixer1.2-dev libupnp-dev libxrandr-dev x11proto-core-dev
   zlib1g-dev
+At least gcc-4.9 is required.
 
 Windows Specific
 ================

cmake/RequireCXXSourceCompiles.cmake

@@ -16,6 +16,6 @@ macro(REQUIRE_CXX_SOURCE_COMPILES _code _var)
 	CHECK_CXX_SOURCE_COMPILES("${_code}" ${_var})
 	if(NOT ${_var})
 		unset(${_var} CACHE)
-		MESSAGE(FATAL_ERROR "${_var} is required for this project to build properly. Aborting.")
+		MESSAGE(FATAL_ERROR "${_var} is required for this project to build properly.${ARGN} Aborting.")
 	endif()
 endmacro()