[PR95720] protect gluefile and wrap_flags with -Wl too

[PR95720] protect gluefile and wrap_flags with -Wl too

The testglue object file gets interpreted as another input file,
changing the dump and aux output names in GCC unless it is protected
by -Wl, like board file-named extra inputs.

Refactor the code that modifies the board settings so that it can be
used to modify regular variables as well, and do so.

for  gcc/testsuite/ChangeLog

	PR testsuite/95720
	* lib/gcc-defs.exp (gcc_adjust_linker_flags_list): Split out of...
	(gcc_adjust_linker_flags): ... this.  Protect gluefile and
	wrap_flags.
	* gcc.misc-tests/outputs.exp: Use gcc_adjust_linker_flags_list.