+ add option to switch off precompiled header

src/Base/CMakeLists.txt

@@ -370,10 +370,10 @@ else(FREECAD_USE_EXTERNAL_ZIPIOS)
 endif(FREECAD_USE_EXTERNAL_ZIPIOS)
 
 
-if(MSVC)
-add_definitions(-D_PreComp_)
-ADD_MSVC_PRECOMPILED_HEADER(FreeCADBase PreCompiled.h PreCompiled.cpp FreeCADBase_CPP_SRCS)
-endif(MSVC)
+if(BUILD_USE_PCH)
+    add_definitions(-D_PreComp_)
+    ADD_MSVC_PRECOMPILED_HEADER(FreeCADBase PreCompiled.h PreCompiled.cpp FreeCADBase_CPP_SRCS)
+endif(BUILD_USE_PCH)
 
 add_library(FreeCADBase SHARED ${FreeCADBase_SRCS})
 

src/Base/Quantity.cpp

@@ -23,9 +23,12 @@
 #include "PreCompiled.h"
 #ifndef _PreComp_
 # include <sstream>
+# ifdef FC_OS_WIN32
+# define _USE_MATH_DEFINES
+# endif // FC_OS_WIN32
+# include <cmath>
 #endif
 
-#include <cmath>
 #include "Quantity.h"
 #include "Exception.h"
 #include "UnitsApi.h"