cmake: add OpenMP support

Author: illwieckz

cmake/DaemonFlags.cmake

@@ -362,6 +362,17 @@ else()
 		endif()
 	endif()
 
+	if (NOT NACL AND BUILD_CLIENT)
+		option(USE_OPENMP "Use OpenMP to parallelize some tasks" OFF)
+
+		if (USE_OPENMP)
+			try_cxx_flag(FOPENMP "-fopenmp")
+			if (NOT FLAG_FOPENMP)
+				message(WARNING "Missing OpenMP")
+			endif()
+		endif()
+	endif()
+
 	if (NACL AND USE_NACL_SAIGO AND SAIGO_ARCH STREQUAL "arm")
 		# This should be set for every build type because build type flags
 		# are set after the other custom flags and then have the last word.