cmake: add USE_FAST_MATH to enable or disable fast math

Author: illwieckz

cmake/DaemonFlags.cmake

@@ -148,6 +148,8 @@ else()
     set(WARNMODE "no-")
 endif()
 
+option(USE_FAST_MATH "Use fast math" ON)
+
 option(USE_DEBUG_FPE "Use floating point exceptions" OFF)
 
 if (USE_DEBUG_FPE)
@@ -157,7 +159,11 @@ endif()
 # Compiler options
 if (MSVC)
     set_c_cxx_flag("/MP")
-    set_c_cxx_flag("/fp:fast")
+
+    if (USE_FAST_MATH)
+        set_c_cxx_flag("/fp:fast")
+    endif()
+
     set_c_cxx_flag("/d2Zi+" RELWITHDEBINFO)
 
     # https://devblogs.microsoft.com/cppblog/msvc-now-correctly-reports-__cplusplus/
@@ -244,7 +250,9 @@ else()
 	endif()
 
 	# Optimizations.
-	set_c_cxx_flag("-ffast-math")
+	if (USE_FAST_MATH)
+		set_c_cxx_flag("-ffast-math")
+	endif()
 
 	if (USE_DEBUG_FPE)
 		# Floating point exceptions requires trapping math