Darwin has case-insensitive filesystems

Darwin has case-insensitive filesystems

HFS+, the FS on Darwin, is case insensitive. So this patch adjusts
filename_cmp.c to ignore the casing when comparing filenames on Darwin.

include/ChangeLog:

        * filenames.h (HAVE_CASE_INSENSITIVE_FILE_SYSTEM): Define
        on Darwin, as well as on the systems that use a DOS-like
        filesystem.

libiberty/ChangeLog:

        * filename_cmp.c (filename_cmp, filename_ncmp): Add handling of
        HAVE_CASE_INSENSITIVE_FILE_SYSTEM.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@175762 138bc75d-0d04-0410-961f-82ee72b054a4