testsuite/arm: add missing -mthumb to several tests

testsuite/arm: add missing -mthumb to several tests

Some tests force -mcpu=cortex-mXX but do not add -mthumb, causing
errors if GCC is not configured to default to Thumb code
(--with-mode=thumb):
cc1: error: target CPU does not support ARM mode

This patch adds -mthumb where relevant.

2020-11-23  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* gcc.target/arm/cortex-m55-nodsp-flag-hard.c: Add -mthumb.
	* gcc.target/arm/cortex-m55-nodsp-flag-softfp.c: Likewise.
	* gcc.target/arm/cortex-m55-nodsp-nofp-flag-softfp.c: Likewise.
	* gcc.target/arm/cortex-m55-nofp-flag-hard.c: Likewise.
	* gcc.target/arm/cortex-m55-nofp-flag-softfp.c: Likewise.
	* gcc.target/arm/cortex-m55-nofp-nomve-flag-softfp.c: Likewise.
	* gcc.target/arm/cortex-m55-nomve-flag-hard.c: Likewise.
	* gcc.target/arm/cortex-m55-nomve-flag-softfp.c: Likewise.
	* gcc.target/arm/cortex-m55-nomve.fp-flag-hard.c: Likewise.
	* gcc.target/arm/cortex-m55-nomve.fp-flag-softfp.c: Likewise.
	* gcc.target/arm/mve/intrinsics/pr97327.c: Likewise.