fix msvc_static_runtime.cmake

Author: jtattermusch

cmake/msvc_static_runtime.cmake

@@ -3,6 +3,8 @@ option(gRPC_MSVC_STATIC_RUNTIME "Link with static msvc runtime libraries" OFF)
 if(gRPC_MSVC_STATIC_RUNTIME)
   # switch from dynamic to static linking of msvcrt
   foreach(flag_var
+    CMAKE_C_FLAGS CMAKE_C_FLAGS_DEBUG CMAKE_C_FLAGS_RELEASE
+    CMAKE_C_FLAGS_MINSIZEREL CMAKE_C_FLAGS_RELWITHDEBINFO
     CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE
     CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)