Fix: Prevent adding /MP flag for MSVC in case any other language than…

… C/CXX will be used (e.g. CUDA)

CMakeLists.txt

@@ -158,11 +158,24 @@ if(CMAKE_COMPILER_IS_MSVC)
     include(ProcessorCount)
     ProcessorCount(CPUCores)
     set(MSVC_MP ${CPUCores} CACHE STRING "Number of simultaneously running compilers (0 = automatic detection by MSVC). See documentation of /MP flag.")
-    if(MSVC_MP EQUAL 0)
-      # MSVC_MP is 0 in case the information cannot be determined by ProcessorCount => fallback
-      add_compile_options("/MP")
-    elseif(MSVC_MP GREATER 1)
-      add_compile_options("/MP${MSVC_MP}")
+    if (CMAKE_VERSION VERSION_LESS 3.11.0)
+      # Usage of COMPILE_LANGUAGE generator expression for MSVC in add_compile_options requires at least CMake 3.11, see https://gitlab.kitware.com/cmake/cmake/issues/17435	  
+      if(MSVC_MP EQUAL 0)
+        # MSVC_MP is 0 in case the information cannot be determined by ProcessorCount => fallback
+        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /MP")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /MP")
+      elseif(MSVC_MP GREATER 1)
+        set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /MP${MSVC_MP}")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /MP${MSVC_MP}")
+      endif()      
+    else()      
+      if(MSVC_MP EQUAL 0)
+        # MSVC_MP is 0 in case the information cannot be determined by ProcessorCount => fallback
+        # Generator expression is necessary to limit /MP flag to C/CXX, so flag will be not set to e.g. CUDA (see https://gitlab.kitware.com/cmake/cmake/issues/17535)
+        add_compile_options($<$<OR:$<COMPILE_LANGUAGE:C>,$<COMPILE_LANGUAGE:CXX>>:/MP>)
+      elseif(MSVC_MP GREATER 1)
+        add_compile_options($<$<OR:$<COMPILE_LANGUAGE:C>,$<COMPILE_LANGUAGE:CXX>>:/MP${MSVC_MP}>)
+      endif()
     endif()
   endif()