testsuite: Fix fam-in-union-alone-in-struct-2.c with unsigned char [PR116148]

testsuite: Fix fam-in-union-alone-in-struct-2.c with unsigned char [PR116148]

As PR116148#c7 shows, fam-in-union-alone-in-struct-2.c still
fails on hppa which is a BE environment, but by checking more
(also confirmed by John in PR116148#c12), it's due to that
signedness of plain char on hppa is signed therefore the value
of with_fam_3_v.a[7] "8f" get sign extended as "ffffff8f" then
the verification will fail.  This patch is to change plain char
with unsigned char to avoid that.

	PR testsuite/116148

gcc/testsuite/ChangeLog:

	* c-c++-common/fam-in-union-alone-in-struct-2.c: Change the type of
	member a[] of union with_fam_3 with unsigned char.