abi: add AddressSpace field to Primitive::Pointer

...and remove it from `PointeeInfo`, which isn't meant for this.

There are still various places (marked with FIXMEs) that assume all pointers
have the same size and alignment. Fixing this requires parsing non-default
address spaces in the data layout string, which will be done in a followup.

compiler/rustc_codegen_gcc/src/common.rs

@@ -211,7 +211,7 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
                 let base_addr = self.const_bitcast(base_addr, self.usize_type);
                 let offset = self.context.new_rvalue_from_long(self.usize_type, offset.bytes() as i64);
                 let ptr = self.const_bitcast(base_addr + offset, ptr_type);
-                if layout.primitive() != Pointer {
+                if !matches!(layout.primitive(), Pointer(_)) {
                     self.const_bitcast(ptr.dereference(None).to_rvalue(), ty)
                 }
                 else {