[Sema][SVE] Allow ?: to select between SVE types in C

When compiling C, a ?: between two values of the same SVE type
currently gives an error such as:

  incompatible operand types ('svint8_t' (aka '__SVInt8_t') and 'svint8_t')

It's supposed to be valid to select between (cv-qualified versions of)
the same SVE type, so this patch adds that case.

These expressions already work for C++ and are tested by
SemaCXX/sizeless-1.cpp.

Differential Revision: https://reviews.llvm.org/D76693