Disable TEST_AFTER_BUILD

This means unit tests won't run with the Build action, but they still will with the explicit Test action. This is for the best, because breakpoints only work when using the latter.
Set PUBLIC_HEADERS_FOLDER_PATH for static libraries by default
Set a default GCC_PREFIX_HEADER
Revert "Set a default GCC_PREFIX_HEADER"

If the file doesn't exist, this causes build failures. Not worth predefining.

This reverts commit a114dfb215e310ba482cba8e86df9d68629d4ef9.
Disable GCC compatibility warnings by default

Clang 4 lyfe!
Add new recommended warnings from the latest LLVM and Xcode 4.6
Alphabetize the warnings, and remove a duplicate.
Merge pull request #2 from jspahrsummers/new-warnings

Add new recommended warnings from the latest LLVM and Xcode 4.6
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Alphabetize the warnings, and remove a duplicate.
  Add new recommended warnings from the latest LLVM and Xcode 4.6
  Disable GCC compatibility warnings by default
  Revert "Set a default GCC_PREFIX_HEADER"
  Set a default GCC_PREFIX_HEADER
  Set PUBLIC_HEADERS_FOLDER_PATH for static libraries by default
  Disable TEST_AFTER_BUILD