testsuite: arm: Use -Os in memset-inline-8* tests

testsuite: arm: Use -Os in memset-inline-8* tests

When the test was initially created, -fcommon was the default, but in
commit r10-4867-g6271dd984d7 the default value changed to -fno-common.
This change made the test start failing. To counter the over-alignment
caused by 'a' no longer being common, use -Os.

gcc/testsuite/ChangeLog:

	* gcc.target/arm/memset-inline-8.c: Use -Os and prefix assembler
	instructions with a tab to improve test stability.
	* gcc.target/arm/memset-inline-8-exe.c: Use -Os.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
(cherry picked from commit 681934aead9c1310e3b910d18986b76272168a80)