Clang: Compile source to /dev/null (instead of overwriting the .o file)

[stevebillings]

Pull Request template

Link to github issue (if applicable):

• The clang extractor's running of the compiler had a side effect: It regenerated the .o (object) files. I don't know if this would ever be a real issue or not, but it certainly doesn't seem like the right thing to do. This change writes all compiler output to /dev/null instead.

If nothing above, what is your reason for this pull request:

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Changes proposed in this pull request:

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[coveralls]

Coverage decreased (-0.01%) to 26.362% when pulling 3752185b2d95aa1460fd16a128fae9cbe3141edf on sb_clangDontOverwriteObjectFiles into b5b4d1da35002014dd0c99f2f89430ff533779ea on master.