cmake: add OpenMP support

Author: illwieckz

cmake/DaemonFlags.cmake

@@ -259,6 +259,10 @@ if (USE_FLOAT_EXCEPTIONS)
     add_definitions(-DDAEMON_USE_FLOAT_EXCEPTIONS)
 endif()
 
+if (NOT NACL AND BUILD_CLIENT)
+	option(USE_OPENMP "Use OpenMP to parallelize some tasks" OFF)
+endif()
+
 if (MSVC)
     set_c_cxx_flag("/MP")
 
@@ -267,6 +271,14 @@ if (MSVC)
         set_cxx_flag("/std:c++23preview")
     endif()
 
+	if (NOT NACL AND BUILD_CLIENT AND USE_OPENMP)
+		try_cxx_flag(OPENMP "/openmp")
+
+		if (NOT FLAG_OPENMP)
+			message(WARNING "Missing OpenMP")
+		endif()
+	endif()
+
     if (USE_FAST_MATH)
         set_c_cxx_flag("/fp:fast")
     else()
@@ -362,6 +374,14 @@ else()
 		endif()
 	endif()
 
+	if (NOT NACL AND BUILD_CLIENT AND USE_OPENMP)
+		try_cxx_flag(FOPENMP "-fopenmp")
+
+		if (NOT FLAG_FOPENMP)
+			message(WARNING "Missing OpenMP")
+		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.