irinterp: Add handling for :throw_undef_if_not (JuliaLang#50303)

This addresses an existing TODO to terminate irinterp on discovering
a :throw_undef_if_not that is dead. The underlying infrastructure to
do this was added in JuliaLang#49692, so this just needed to be wired up
properly.

base/compiler/ssair/irinterp.jl

@@ -130,8 +130,16 @@ function reprocess_instruction!(interp::AbstractInterpreter, idx::Int, bb::Union
             if nothrow
                 ir.stmts[idx][:flag] |= IR_FLAG_NOTHROW
             end
-        elseif head === :throw_undef_if_not || # TODO: Terminate interpretation early if known false?
-               head === :gc_preserve_begin ||
+        elseif head === :throw_undef_if_not
+            condval = maybe_extract_const_bool(argextype(inst.args[2], ir))
+            condval isa Bool || return false
+            if condval
+                ir.stmts[idx][:inst] = nothing
+                # We simplified the IR, but we did not update the type
+                return false
+            end
+            rt = Union{}
+        elseif head === :gc_preserve_begin ||
                head === :gc_preserve_end
             return false
         else