testsuite: Restore TORTURE_OPTIONS in gm2/warnings/returntype/fail/warnings-returntyp...

testsuite: Restore TORTURE_OPTIONS in gm2/warnings/returntype/fail/warnings-returntype-fail.exp

Between 20230126 and 20230127, 1100+ gm2 tests started to FAIL for the
non-default multilib, e.g.

FAIL: gm2/calling-c/datatypes/unbounded/run/pass/m.mod compilation,
{additional_flags= -O0 -g -Werror=return-type } timeout=10
UNRESOLVED: gm2/calling-c/datatypes/unbounded/run/pass/m.mod execution,
{additional_flags= -O0 -g -Werror=return-type } timeout=10
FAIL: gm2/case/pass/testcase1.mod,  -O0 -g -Werror=return-type
[...]
cc1gm2: warning: '-Werror=' argument '-Werror=return-type' is not valid for
Modula-2

I'm seeing this on all of Solaris/x86, Solaris/SPARC, and Linux/x86_64.

I could trace this to
gm2/warnings/returntype/fail/warnings-returntype-fail.exp not properly
restoring TORTURE_OPTIONS.

Tested on i386-pc-solaris2.11 and sparc-sun-solaris2.11.

2023-01-30  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/testsuite:
	* gm2/warnings/returntype/fail/warnings-returntype-fail.exp: Save,
	restore TORTURE_OPTIONS.