bitint: Handle VIEW_CONVERT_EXPRs between large/huge BITINT_TYPEs and VECTOR/COMPLEX_...

bitint: Handle VIEW_CONVERT_EXPRs between large/huge BITINT_TYPEs and VECTOR/COMPLEX_TYPE etc. [PR114073]

The following patch implements support for VIEW_CONVERT_EXPRs from/to
large/huge _BitInt to/from vector or complex types or anything else but
integral/pointer types which doesn't need to live in memory.

2024-02-24  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/114073
	* gimple-lower-bitint.cc (bitint_large_huge::lower_stmt): Handle
	VIEW_CONVERT_EXPRs between large/huge _BitInt and non-integer/pointer
	types like vector or complex types.
	(gimple_lower_bitint): Don't merge VIEW_CONVERT_EXPRs to non-integral
	types.  Fix up VIEW_CONVERT_EXPR handling.  Allow merging
	VIEW_CONVERT_EXPR from non-integral/pointer types with a store.

	* gcc.dg/bitint-93.c: New test.