PR/18555
        * gcc.h (DEFAULT_WORD_SWITCH_TAKES_ARG): Add isysroot.
        * config/darwin-c.c (darwin_register_frameworks): Use sysroot.

        testsuite
        * gcc.dg/cpp/isysroot-1.c: New test.
        * gcc.dg/cpp/usr/include/stdio.h: New file.
        * gcc.dg/cpp/isysroot-2.c: New test.
        * gcc.dg/cpp/System/Library/Framework/Carbon.framework/Headers/Carbon.h:
        New file.

From-SVN: r91178