Stack Limit as an Argument Purpose (#372)

* Initial approach.

* Move stack_limit check before opening the frame

* Account for GPRs and frame pointer in stack check

* Check stack_limit example.

* Remove stack_limit attribute code.

Amends #359

* fmt

lib/codegen/src/context.rs

@@ -297,10 +297,6 @@ impl Context {
 
     /// Insert prologue and epilogues after computing the stack frame layout.
     pub fn prologue_epilogue(&mut self, isa: &TargetIsa) -> CodegenResult<()> {
-        assert!(
-            self.func.stack_limit.is_none(),
-            "stack_limit isn't implemented yet"
-        );
         isa.prologue_epilogue(&mut self.func)?;
         self.verify_if(isa)?;
         self.verify_locations_if(isa)?;