arm: add extra sizes to Wstrinop-overflow-47.c warning tests

A thumb2 target without a FPU like -mcpu=cortex-m3 will generate
'vector(4) char' stores which lead to warnings with sizes that weren't being
allowed before by the test.  This patch adds these sizes.

gcc/testsuite/ChangeLog:

	* gcc.dg/Wstringop-overflow-47.c: Adjust warnings to allow for 32-bit
	stores.