[gdb/testsuite] Handle ada in gdb_compile_shlib

[gdb/testsuite] Handle ada in gdb_compile_shlib

The single test-case in the testsuite that creates an ada shared library is
gdb.ada/catch_ex_std.exp.

The test-case does use gdb_compile_shlib, but with a few tweaks that make sure
things are properly handled for ada.

Move the ada-specific code to gdb_compile_shlib, such that gdb_compile_sh can
be used for ada shared libs without tweaks.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-12-13  Tom de Vries  <tdevries@suse.de>

	* lib/gdb.exp (gdb_compile_shlib): Handle ada.
	* gdb.ada/catch_ex_std.exp: Use gdb_compile_shlib to compile from
	source to shared lib.  Add ada to options.