-mno-long-calls for expected regalloc in arm/fp16-aapcs-2.c test

-mno-long-calls for expected regalloc in arm/fp16-aapcs-2.c test

The implicit -mlong-calls used in our arm-vxworks configurations
changes the register allocation patterns in the arm/fp16-aapcs-2.c
test: r3 ends up used in the long-call sequence, and we end up using
ip as a temporary, which doesn't match the expected mov patterns.

This patch adds an explicit -mno-long-calls for the generated code to
match the expectation.

for  gcc/testsuite/ChangeLog

	* gcc.target/arm/fp16-aapcs-2.c: Use -mno-long-calls.