[PATCH] Permit OpenCL event_t's to be constructed from integer value 0.

[Neil Henning]

  Also, ran check-all tests, results as below;
    Neils-MacBook-Air:build neil$ ninja check-all
    [1/1] Running all regression tests
    lit.py: lit.cfg:196: note: using clang: '/Users/neil/repo/llvm/build/./bin/clang'
    lit.py: lit.cfg:440: note: using SDKROOT: '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk'
    -- Testing: 16740 tests, 4 threads --
    Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
    Testing Time: 403.83s
      Expected Passes    : 16501
      Expected Failures  : 74
      Unsupported Tests  : 165

http://llvm-reviews.chandlerc.com/D2860