env: Bail out if CPATH and friends are set

If CPATH, C_INCLUDE_PATH, CPLUS_INCLUDE_PATH, or OBJC_INCLUDE_PATH are set, bail out.
These environment variables are known to break crosstool-ng's build.

This closes #327

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>

scripts/crosstool-NG.sh.in

@@ -55,6 +55,10 @@ CT_DoLog INFO "Performing some trivial sanity checks"
 CT_TestAndAbort "Don't set LD_LIBRARY_PATH. It screws up the build." -n "${LD_LIBRARY_PATH}"
 CT_TestAndAbort "Don't set LIBRARY_PATH. It screws up the build." -n "${LIBRARY_PATH}"
 CT_TestAndAbort "Don't set LPATH. It screws up the build." -n "${LPATH}"
+CT_TestAndAbort "Don't set CPATH. It screws up the build." -n "${CPATH}"
+CT_TestAndAbort "Don't set C_INCLUDE_PATH. It screws up the build." -n "${C_INCLUDE_PATH}"
+CT_TestAndAbort "Don't set CPLUS_INCLUDE_PATH. It screws up the build." -n "${CPLUS_INCLUDE_PATH}"
+CT_TestAndAbort "Don't set OBJC_INCLUDE_PATH. It screws up the build." -n "${OBJC_INCLUDE_PATH}"
 CT_TestAndAbort "Don't set CFLAGS. It screws up the build." -n "${CFLAGS}"
 CT_TestAndAbort "Don't set CXXFLAGS. It screws up the build." -n "${CXXFLAGS}"
 CT_Test "GREP_OPTIONS screws up the build. Resetting." -n "${GREP_OPTIONS}"