testsuite: Add RISC-V to targets not xfailing gcc.dg/attr-alloc_size-11.c:50,51.

testsuite: Add RISC-V to targets not xfailing gcc.dg/attr-alloc_size-11.c:50,51.

The test has been observed to pass on most architectures including RISC-V:
https://godbolt.org/z/8nYEvW6n1

Origin issue see:
https://gcc.gnu.org/PR79356#c11

Update RISC-V target to the pass list.

gcc/testsuite/ChangeLog:

	* gcc.dg/attr-alloc_size-11.c: Add RISC-V to the list
	of targets excluding xfail on lines 50 and 51.