Fix VLA printing for Ada

Fix VLA printing for Ada

While looking at a different Ada problem, I found that printing a
record containing a VLA did not work properly.

I tracked the problem down to dwarf2_evaluate_property trying, and
failing, to compare two types that differed only in qualifiers.

This patch changes dwarf2_evaluate_property to ignore qualifiers when
comparing types.

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-05-08  Tom Tromey  <tromey@adacore.com>

	* dwarf2loc.c (dwarf2_evaluate_property) <PROP_ADDR_OFFSET>:
	Compare main types.

gdb/testsuite/ChangeLog
2019-05-08  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/vla.exp: New file.
	* gdb.ada/vla/vla.adb: New file.