Auto merge of #142911 - mejrs:unsized, r=compiler-errors

Remove support for dynamic allocas

Followup to rust-lang/rust#141811

compiler/rustc_codegen_gcc/src/builder.rs

@@ -926,10 +926,6 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
             .get_address(self.location)
     }
 
-    fn dynamic_alloca(&mut self, _len: RValue<'gcc>, _align: Align) -> RValue<'gcc> {
-        unimplemented!();
-    }
-
     fn load(&mut self, pointee_ty: Type<'gcc>, ptr: RValue<'gcc>, align: Align) -> RValue<'gcc> {
         let block = self.llbb();
         let function = block.get_function();