arm: testsuite: tweak bics_3.c [PR113542]

arm: testsuite: tweak bics_3.c [PR113542]

This test was too simple, which meant that the compiler was sometimes
able to find a better optimization of the code than using a BICS
instruction.  Fix this by changing the test slightly to produce a
sequence where BICS should always be the preferred solution.

gcc/testsuite:
	PR target/113542
	* gcc.target/arm/bics_3.c: Adjust code to something which should
	always result in BICS.