With submodules and coarrays, name mangling results in long internal
symbols.  Enlarge internal buffer.

gcc/fortran/
	PR fortran/95827
	* iresolve.c (gfc_get_string): Enlarge internal buffer used in
	generating the mangled name.

(cherry picked from commit a16d0924f18046704ef9a4b6d9593718594677f1)