arm: force use of r4 for __gnu_cmse_nonsecure_call when !FPCXT [PR99271]

arm: force use of r4 for __gnu_cmse_nonsecure_call when !FPCXT [PR99271]

Commit r10-6017 relaxed the constraint on thumb2 calls to
__gnu_cmse_nonsecure_call to allow any register for the call address.
Although the initial code expansion continues to use r4 with the FPCXT
extension is not enabled, the change was unsafe because subsequent
optimizations could use the additional freedom to change which
register was being used.

To fix this we need to split the output patterns in the machine
description to use distinct recognizers: one with the additional
freedom when FPCXT is enabled an another that retains the original
restrictions when the extension is not available.

gcc:
	PR target/99271
	* config/arm/thumb2.md (nonsecure_call_reg_thumb2_fpcxt): New pattern.
	(nonsecure_call_value_reg_thumb2_fpcxt): Likewise.
	(nonsecure_call_reg_thumb2): Restrict to using r4 for the callee
	address and disable when the FPCXT is not available.
	(nonsecure_call_value_reg_thumb2): Likewise.

gcc/testsuite:
	* gcc.target/arm/cmse/cmse-18.c: New test.