arm: Fix multilib mapping for CDE extensions [PR100856]

arm: Fix multilib mapping for CDE extensions [PR100856]

This is a followup to Srinath's recent patch: the newly added test is
failing e.g. on arm-linux-gnueabihf without R/M profile multilibs.

It is also failing on arm-eabi with R/M profile multilibs if the
execution engine does not support v8.1-M instructions.

The patch avoids this by adding check_effective_target_FUNC_multilib
in target-supports.exp which effectively checks whether the target
supports linking and execution, like what is already done for other
ARM effective targets.  pr100856.c is updated to use it instead of
arm_v8_1m_main_cde_mve_ok (which makes the testcase a bit of a
duplicate with check_effective_target_FUNC_multilib).

In addition, I noticed that requiring MVE does not seem necessary and
this enables the test to pass even when targeting a CPU without MVE:
since the test does not involve actual CDE instructions, it can pass
on other architecture versions.  For instance, when requiring MVE, we
have to use cortex-m55 under QEMU for the test to pass because the
memset() that comes from v8.1-m.main+mve multilib uses LOB
instructions (DLS) (memset is used during startup).  Keeping
arm_v8_1m_main_cde_mve_ok would mean we would enable the test provided
we have the right multilibs, causing a runtime error if the simulator
does not support LOB instructions (e.g. when targeting cortex-m7).

I do not update sourcebuild.texi since the CDE effective targets are
already collectively documented.

Finally, the patch fixes two typos in comments.

2021-07-15  Christophe Lyon  <christophe.lyon@foss.st.com>

	PR target/100856
	gcc/
	* config/arm/arm.opt: Fix typo.
	* config/arm/t-rmprofile: Fix typo.

	gcc/testsuite/
	* gcc.target/arm/acle/pr100856.c: Use arm_v8m_main_cde_multilib
	and arm_v8m_main_cde.
	* lib/target-supports.exp: Add
	check_effective_target_FUNC_multilib for ARM CDE.