runtime: mark go-context.S as no-executable-stack and split-stack supported

    
    The .note.GNU-stack section tells the linker that this object does not
    require an executable stack.
    
    The .note.GNU-split-stack section tells the linker that functions in
    this object can be called directly by split-stack functions, without
    require a large stack.
    
    The .note.GNU-no-split-stack section tells the linker that functions
    in this object do not have a split-stack prologue.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/198440

From-SVN: r276488

gcc/go/gofrontend/MERGE

-07faafda5fbd66a710153814f30d93c91461e7cb
+a3aef6b6df932ea6c7094d074695bc0b033a3d17
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/go-context.S

@@ -66,4 +66,8 @@ __go_makecontext:
 
 	ret
 
+	.section	.note.GNU-stack,"",@progbits
+	.section	.note.GNU-split-stack,"",@progbits
+	.section	.note.GNU-no-split-stack,"",@progbits
+
 #endif