[CodeGen] Create IFUNCs in the program address space, not hard-coded 0 (#105726)
Commit 0d527e56a5ee ("GlobalIFunc: Make ifunc respect function address
spaces") added support for this within LLVM, but Clang does not properly
honour the target's address spaces when creating IFUNCs, crashing with
RAUW and verifier assertion failures when compiling C code on a target
with a non-zero program address space, so fix this.