[gdb/testsuite] Make noclone conditional in vla-optimized-out.c

[gdb/testsuite] Make noclone conditional in vla-optimized-out.c

Make the noclone attribute on f1 in vla-optimized-out.c conditional.  This
makes the test-case by default identical to
gcc/testsuite/gcc.dg/guality/vla-1.c.

Tested on x86_64-linux.

2018-07-20  Tom de Vries  <tdevries@suse.de>

	* gdb.base/vla-optimized-out.c: Make noclone attribute conditional on
	NOCLONE macro.
	* gdb.base/vla-optimized-out.exp: Use additional_flags -DNOCLONE.