Fix builds with mingw x86 and x86_64.

- Deal with tmpnam_s() preproc issues in file_util.cc
  when building with mingw-w64..
- Add stdint.h include in mkvmuxer.cc.

Change-Id: I819a27e6d805d772a6e1863982a2eeafd27b2a0d
2 files changed