Fix Compiling model with g++ fails with "cc1plus: fatal error: -pch: No such file or directory" #583

[seantalts]

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• Run tests: ./runCmdStanTests.py src/test
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[sakrejda]

Yep, that's the thing. Do we have a test on Jenkins or something that will fail if compiling with g++ doesn't work?

[seantalts]

Not yet - #591 will test with g++4.9 on Windows once we fix those tests up.