msvc_runtime.cmake: Check for MSVC, not WIN32.
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

webmproject/libwebm,webmproject/libwebm,webmproject/libwebm