[Backport,4.7,committed]: Fix PR other/52545: SECTION_EXCLUE clobbers SECTION_MACH_DEP

[Georg-Johann Lay]

http://gcc.gnu.org/viewcvs?view=revision&revision=185685

Applied as obvious.

Johann

        Backport from mainline r185259.

        PR other/52545
        * output.h (SECTION_EXCLUDE, SECTION_MACH_DEP): Don't use
        SECTION_MACH_DEP reserved bits for SECTION_EXCLUDE.