Make shared libraries be able to link to MSVC static runtime libraries, so that VC runtime is not required.

cmake/CMakeLists.txt

@@ -40,8 +40,6 @@ else (BUILD_SHARED_LIBS)
 endif (BUILD_SHARED_LIBS)
 option(protobuf_BUILD_SHARED_LIBS "Build Shared Libraries" ${protobuf_BUILD_SHARED_LIBS_DEFAULT})
 include(CMakeDependentOption)
-cmake_dependent_option(protobuf_MSVC_STATIC_RUNTIME "Link static runtime libraries" ON
-  "NOT protobuf_BUILD_SHARED_LIBS" OFF)
 set(protobuf_WITH_ZLIB_DEFAULT ON)
 option(protobuf_WITH_ZLIB "Build with zlib support" ${protobuf_WITH_ZLIB_DEFAULT})
 set(protobuf_DEBUG_POSTFIX "d"
@@ -155,22 +153,22 @@ if (protobuf_BUILD_SHARED_LIBS)
   set(protobuf_SHARED_OR_STATIC "SHARED")
 else (protobuf_BUILD_SHARED_LIBS)
   set(protobuf_SHARED_OR_STATIC "STATIC")
-  # In case we are building static libraries, link also the runtime library statically
-  # so that MSVCR*.DLL is not required at runtime.
-  # https://msdn.microsoft.com/en-us/library/2kzt1wy3.aspx
-  # This is achieved by replacing msvc option /MD with /MT and /MDd with /MTd
-  # http://www.cmake.org/Wiki/CMake_FAQ#How_can_I_build_my_MSVC_application_with_a_static_runtime.3F
-  if (MSVC AND protobuf_MSVC_STATIC_RUNTIME)
-    foreach(flag_var
-        CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE
-        CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)
-      if(${flag_var} MATCHES "/MD")
-        string(REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}")
-      endif(${flag_var} MATCHES "/MD")
-    endforeach(flag_var)
-  endif (MSVC AND protobuf_MSVC_STATIC_RUNTIME)
 endif (protobuf_BUILD_SHARED_LIBS)
 
+# In case we are linking the runtime library statically so that MSVCR*.DLL is not required at runtime.
+# https://msdn.microsoft.com/en-us/library/2kzt1wy3.aspx
+# This is achieved by replacing msvc option /MD with /MT and /MDd with /MTd
+# http://www.cmake.org/Wiki/CMake_FAQ#How_can_I_build_my_MSVC_application_with_a_static_runtime.3F
+if (MSVC AND protobuf_MSVC_STATIC_RUNTIME)
+  foreach(flag_var
+      CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE
+      CMAKE_CXX_FLAGS_MINSIZEREL CMAKE_CXX_FLAGS_RELWITHDEBINFO)
+    if(${flag_var} MATCHES "/MD")
+      string(REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}")
+    endif(${flag_var} MATCHES "/MD")
+  endforeach(flag_var)
+endif (MSVC AND protobuf_MSVC_STATIC_RUNTIME)
+
 if (MSVC)
   # Build with multiple processes
   add_definitions(/MP)