cmd/compile: ssa/debug_test.go very regressed on Linux (but not OSX)

[dr2chase]

I noticed this last night while trying to throughly test the changes to prologue end and DWARF version.
It appears to be some interaction with some other change, and no idea yet why it works on OSX.

Everything after a call to Fprintf or println is missing; if done by hand, the debugger races to the end.

    --- FAIL: TestNexting/gdb-opt-hist (1.63s)
    	debug_test.go:234: step/next histories differ, diff=
    		--- testdata/hist.gdb-opt.nexts	2018-05-22 06:09:57.601443878 -0400
    		+++ /tmp/debug_test255923597/test-hist.gdb-opt.nexts	2018-05-22 06:12:09.156909059 -0400
    		@@ -123,39 +123,3 @@
    		 91:			n += a
    		 90:			t += i * a
    		 92:			fmt.Fprintf(os.Stderr, "%d\t%d\t%d\t%d\t%d\n", i, a, n, i*a, t) //gdb-dbg=(n,i,t)
    		-86:		for i, a := range hist {
...
    		-86:		for i, a := range hist {
    		-98:	}

[gopherbot]

Change https://golang.org/cl/114080 mentions this issue: cmd/compile: grow stack before test() to avoid gdb misbehavior