cmd/compile: regenerate builtin.go

Following a recent change, file builtin.go is not up-to-date.
Generate it again by running go generate.

Fixes #13203

Change-Id: Ib91c5ccc93665c043da95c7d3783ce5d94e48466
Reviewed-on: https://go-review.googlesource.com/16821
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: dspezia

src/cmd/compile/internal/gc/builtin.go

@@ -4,7 +4,6 @@ package gc
 
 const runtimeimport = "" +
 	"package runtime\n" +
-	"import runtime \"runtime\"\n" +
 	"func @\"\".newobject (@\"\".typ·2 *byte) (? *any)\n" +
 	"func @\"\".panicindex ()\n" +
 	"func @\"\".panicslice ()\n" +
@@ -162,7 +161,6 @@ const runtimeimport = "" +
 
 const unsafeimport = "" +
 	"package unsafe\n" +
-	"import runtime \"runtime\"\n" +
 	"type @\"\".Pointer uintptr\n" +
 	"func @\"\".Offsetof (? any) (? uintptr)\n" +
 	"func @\"\".Sizeof (? any) (? uintptr)\n" +