cmd/compile: fix gdb stepping test

Not sure why this changed behavior, but seems mostly harmless.

Fixes #28198

Change-Id: Ie25c6e1fcb64912a582c7ae7bf92c4c1642e83cb
Reviewed-on: https://go-review.googlesource.com/c/141649Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/ssa/testdata/hist.gdb-opt.nexts

@@ -120,6 +120,7 @@ t = 0
 a = 3
 n = 0
 t = 0
+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)
 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)
@@ -128,6 +129,7 @@ t = 0
 a = 3
 n = 3
 t = 3
+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)
 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)
@@ -141,6 +143,7 @@ t = 9
 a = 2
 n = 6
 t = 9
+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)
 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)
@@ -149,6 +152,7 @@ t = 9
 a = 1
 n = 8
 t = 17
+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)
 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)