aarch64: SVE: ICE in expand_direct_optab_fn [PR98177]

aarch64: SVE: ICE in expand_direct_optab_fn [PR98177]

Problem comes from using the wrong interface to get the index type for a
COND_REDUCTION. For fixed-length SVE we get a V2SI (a 64-bit Advanced
SIMD vector) instead of a VNx2SI (an SVE vector that stores SI elements
in DI containers).

Credits to Richard Sandiford for pointing out the issue's root cause.

Original PR snippet proposed to reproduce issue was only causing ICE for C++
compiler (see pr98177-1 test cases). I've slightly modified original
snippet in order to reproduce issue on both C and C++ compilers. These
are pr98177-2 test cases.

gcc/ChangeLog:

	PR target/98177
	* tree-vect-loop.c (vect_create_epilog_for_reduction): Use
	get_same_sized_vectype to obtain index type.
	(vectorizable_reduction): Likewise.

gcc/testsuite/ChangeLog:

	PR target/98177
	* g++.target/aarch64/sve/pr98177-1.C: New test.
	* g++.target/aarch64/sve/pr98177-2.C: New test.
	* gcc.target/aarch64/sve/pr98177-1.c: New test.
	* gcc.target/aarch64/sve/pr98177-2.c: New test.