[COMMITTED] Fix PR aarch64/104474: ICE with vector float initializers and non-consts.

[COMMITTED] Fix PR aarch64/104474: ICE with vector float initializers and non-consts.

The problem here is that the aarch64 back-end was placing const0_rtx
into the constant vector RTL even if the mode was a floating point mode.
The fix is instead to use CONST0_RTX and pass the mode to select the
correct zero (either const_int or const_double).

Committed as obvious after a bootstrap/test on aarch64-linux-gnu with
no regressions.

	PR target/104474

gcc/ChangeLog:

	* config/aarch64/aarch64.cc
	(aarch64_sve_expand_vector_init_handle_trailing_constants):
	Use CONST0_RTX instead of const0_rtx for the non-constant elements.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/pr104474-1.c: New test.
	* gcc.target/aarch64/sve/pr104474-2.c: New test.
	* gcc.target/aarch64/sve/pr104474-3.c: New test.