Update test cases that work with minimal encodings

Update test cases that work with minimal encodings

Some test cases already work fine with minimal encodings (in some
cases perhaps due to the variant parts series) This patch updates
these tests as appropriate.

gdb/testsuite/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/frame_arg_lang.exp: Run with multiple -fgnat-encodings
	values.
	* gdb.ada/funcall_ref.exp: Run with multiple -fgnat-encodings
	values.  Update test for minimal encodings.
	* gdb.ada/lang_switch.exp: Update test for minimal encodings.
	* gdb.ada/var_rec_arr.exp: Run with multiple -fgnat-encodings
	values.  Update test for minimal encodings.