msvc_runtime.cmake: Check for MSVC, not WIN32.

- The flag change here is supposed to target only MSVC builds,
  and not all Windows builds.
- Style tweak to match other CMake files.

Change-Id: I664705e13d810e2d41422eae655b5a68ff244308

build/msvc_runtime.cmake

@@ -7,7 +7,7 @@
 ##  be found in the AUTHORS file in the root of the source tree.
 cmake_minimum_required(VERSION 2.8)
 
-if(WIN32)
+if (MSVC)
   # CMake defaults to producing code linked to the DLL MSVC runtime. In libwebm
   # static is typically desired. Force static code generation unless the user
   # running CMake set MSVC_RUNTIME to dll.
@@ -19,6 +19,5 @@ if(WIN32)
         string(REGEX REPLACE "/MD" "/MT" ${flag_var} "${${flag_var}}")
       endif (${flag_var} MATCHES "/MD")
     endforeach (flag_var)
-  endif(NOT "${MSVC_RUNTIME}" STREQUAL "dll")
-endif(WIN32)
-
+  endif ()
+endif ()