MSVC: Factor out initialization of /GR flag

Modules/Platform/Windows-MSVC.cmake

@@ -163,6 +163,8 @@ foreach(lang C CXX)
   endif()
 endforeach()
 
+set(_GR " /GR")
+
 if(WINCE)
   foreach(lang C CXX)
     string(TOUPPER "${_MSVC_${lang}_ARCHITECTURE_FAMILY}" _MSVC_${lang}_ARCHITECTURE_FAMILY_UPPER)
@@ -182,7 +184,7 @@ if(WINCE)
 
   set(_RTC1 "")
   set(_FLAGS_C "")
-  set(_FLAGS_CXX " /GR /EHsc")
+  set(_FLAGS_CXX "${_GR} /EHsc")
 
   foreach(lang C CXX)
     if(_MSVC_${lang}_ARCHITECTURE_FAMILY STREQUAL "ARM")
@@ -204,7 +206,7 @@ if(WINCE)
 elseif(WINDOWS_PHONE OR WINDOWS_STORE)
   set(_PLATFORM_DEFINES "/DWIN32")
   set(_FLAGS_C " /DUNICODE /D_UNICODE")
-  set(_FLAGS_CXX " /DUNICODE /D_UNICODE /GR /EHsc")
+  set(_FLAGS_CXX " /DUNICODE /D_UNICODE${_GR} /EHsc")
   if(WINDOWS_STORE AND MSVC_VERSION GREATER 1899)
     set(CMAKE_C_STANDARD_LIBRARIES_INIT "WindowsApp.lib")
   elseif(WINDOWS_PHONE)
@@ -226,12 +228,12 @@ else()
       set(_FLAGS_CXX " -frtti -fexceptions")
     else()
       set(_RTC1 "/RTC1")
-      set(_FLAGS_CXX " /GR /EHsc")
+      set(_FLAGS_CXX "${_GR} /EHsc")
     endif()
     set(CMAKE_C_STANDARD_LIBRARIES_INIT "kernel32.lib user32.lib gdi32.lib winspool.lib shell32.lib ole32.lib oleaut32.lib uuid.lib comdlg32.lib advapi32.lib")
   else()
     set(_RTC1 "/GZ")
-    set(_FLAGS_CXX " /GR /GX")
+    set(_FLAGS_CXX "${_GR} /GX")
     set(CMAKE_C_STANDARD_LIBRARIES_INIT "kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib")
   endif()
 
@@ -241,6 +243,8 @@ else()
   endif()
 endif()
 
+unset(_GR)
+
 set(CMAKE_CXX_STANDARD_LIBRARIES_INIT "${CMAKE_C_STANDARD_LIBRARIES_INIT}")
 
 # executable linker flags