Revert "stdenv: set correct compiler symbol for gcc 4.0"

This reverts commit f4dc5614953b3b90acc28c83262d56587b0616b1.
Revert "default_compiler: recognize gcc-4.0"

This reverts commit bedcbb806bb8a991a1317b4ccde8d16b6974cc46.
Revert "default_cc: locate already returns Pathnames"

This reverts commit 8ec6123d439e8f4d3586bbca6a426b726bd5e9dd.
Revert "stdenv: fix self.cc check"

This reverts commit 0e1d52c0d3945ae0ac69383c7734e425b7fbf8f1.