cmd/compile: generate frame pointers for otherwise frameless functions

func f() {
    g()
}

We mistakenly don't add a frame pointer for f.  This means f
isn't seen when walking the frame pointer linked list.  That
matters for kernel-gathered profiles, and is an impediment for
issues like #16638.

To fix, allocate a stack frame even for otherwise frameless functions
like f.  It is a bit tricky because we need to avoid some runtime
internals that really, really don't want one.

No test at the moment, as only kernel CPU profiles would catch it.
Tests will come with the implementation of #16638.

Fixes #18103

Change-Id: I411206cc9de4c8fdd265bee2e4fa61d161ad1847
Reviewed-on: https://go-review.googlesource.com/33754
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

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

@@ -380,6 +380,9 @@ func compile(fn *Node) {
 	if fn.Func.Wrapper {
 		ptxt.From3.Offset |= obj.WRAPPER
 	}
+	if fn.Func.NoFramePointer {
+		ptxt.From3.Offset |= obj.NOFRAME
+	}
 	if fn.Func.Needctxt {
 		ptxt.From3.Offset |= obj.NEEDCTXT
 	}