testsuite, Darwin: Skip g++.dg/debug/dwarf2/pr85550.C

testsuite, Darwin: Skip g++.dg/debug/dwarf2/pr85550.C

There are two problems here; first that the emitted asm for
-fdebug-types-section is ELF-specfic leading to assembler errors for
Mach-O.  If we fix this, we get a secondary fail since the debug linker
does not recognise DW_FORM_ref_sig8.  Disable ths test until we get
DWARF-5 support in the external Darwin toolchain components.

gcc/testsuite/ChangeLog:

	* g++.dg/debug/dwarf2/pr85550.C: Skip for Darwin.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit 76547f4c97b1c0744487d624c5e2e5a15d0370a9)