gdb.ada/info_exc.exp,mi_exc_info.exp: Use more unique exception name.

In the case where the GNAT runtime was built with full debugging info,
several of the exceptions defined there might have a name contain
the word "global". To make this less likely, this patch renames
the exception name, replacing "Global" by "Global_GDB". It still
keeps the exeption name relatively short, while it is unlikely that
the GNAT runtime has an exception whose name explicitly mentions GDB,
and even less likely that it contains "Global_GDB".

gdb/testsuite/ChangeLog:

        * info_exc/const.ads (Aint_Global_GDB_E): Renames Aint_Global_E.
        * info_exc/foo.adb: Adjust to new exception name.
        * info_exc.exp: Adjust after exception renaming in const.ads.
        Update "info exception global" test to test "info exceptions
        global_gdb" instead.

        * mi_exc_info/const.ads (Aint_Global_GDB_E): Renames Aint_Global_E.
        * mi_exc_info/foo.adb (Adjust to new exception name.
        * mi_exc_info.exp: Adjust after exception renaming in const.ads.
        Update "-info-ada-exceptions global" test to test
        "-info-ada-exceptions global_gdb" instead.