gdb/testsuite: Allow cc-with-tweaks board file to be used with Fortran

gdb/testsuite: Allow cc-with-tweaks board file to be used with Fortran

The board file cc-with-tweaks is used as the core for lots of other
board files, for example cc-with-gdb-index and cc-with-debug-names.
This commit extends cc-with-tweaks so that it will wrap the Fortran
compiler, allowing for more test coverage.

I tested all of the board files that make use of cc-with-tweaks
running the gdb.fortran/*.exp test set, and in some cases I did see
extra failures.  The "standard" results are:

                    === gdb Summary ===

    # of expected passes            953
    # of known failures             2

With board file 'cc-with-dwz-m':

                    === gdb Summary ===

    # of expected passes            903
    # of unexpected failures        1
    # of known failures             2
    # of untested testcases         4

With board file 'dwarf4-gdb-index':

                    === gdb Summary ===

    # of expected passes            950
    # of unexpected failures        3
    # of known failures             2

With board file 'fission-dwp':

                    === gdb Summary ===

    # of expected passes            949
    # of unexpected failures        4
    # of known failures             2

Despite these extra failure I don't think this should prevent this
change going in as these failures presumably already exist in GDB.

gdb/testsuite/ChangeLog:

	* boards/cc-with-tweaks.exp: Setup F90_FOR_TARGET and
	F77_FOR_TARGET.

Change-Id: I06d412f94d0e119ad652dd6c20829f6705a54622