arm: [testsuite] Skip thumb2-cond-cmp tests on Cortex-M [PR94595]

arm: [testsuite] Skip thumb2-cond-cmp tests on Cortex-M [PR94595]

Since r204778 (g571880a0a4c512195aa7d41929ba6795190887b2), we favor
branches over IT blocks on Cortex-M. As a result, instead of
generating two nested IT blocks in thumb2-cond-cmp-[1234].c, we
generate either a single IT block, or use branches depending on
conditions tested by the program.

Since this was a deliberate change and the tests still pass as
expected on Cortex-A, this patch skips them when targetting
Cortex-M. The avoids the failures on Cortex M3, M4, and M33.  This
patch makes the testcases unsupported on Cortex-M7 although they pass
in this case because this CPU has different branch costs.

I tried to relax the scan-assembler directives using eg. cmpne|subne
or cmpgt|ble but that seemed fragile.

2020-09-07  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	PR target/94595
	* gcc.target/arm/thumb2-cond-cmp-1.c: Skip if arm_cortex_m.
	* gcc.target/arm/thumb2-cond-cmp-2.c: Skip if arm_cortex_m.
	* gcc.target/arm/thumb2-cond-cmp-3.c: Skip if arm_cortex_m.
	* gcc.target/arm/thumb2-cond-cmp-4.c: Skip if arm_cortex_m.