[gdb/testsuite] Avoid gnatbind/gnatlink in gdb.ada/catch_ex_std.exp

[gdb/testsuite] Avoid gnatbind/gnatlink in gdb.ada/catch_ex_std.exp

There's a single test-case in the testsuite that explicitly calls gnatbind and
gnatlink: gdb.ada/catch_ex_std.exp.

Instead, use gnatmake and pass specific gnatbind and gnatlink options using
gnatmake passthrough options -bargs and -largs.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

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

	* gdb.ada/catch_ex_std.exp: Use gnatmake -bargs and -largs instead of
	calling gnatbind and gnatlink.