Revert new OS and CC detection and related changes since r15923.

Revert "Attempt to fix leftover test breakage on Mac."
Revert "Fix d8 build error when V8_SHARED is unset on Linux."
Revert "Fix V8_GNUC_PREREQ macro."
Revert "Fix typo."
Revert "Implement correct OS and CC detection."

TBR=svenpanne@chromium.org,danno@chromium.org

Review URL: https://codereview.chromium.org/21022003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15932 ce2b1a6d-e550-0410-aec6-3dcde31c8c00