cmd/compile: fix lineno restoration after SSA compilation

cmd/compile: fix lineno restoration after SSA compilation

Without SSA:

$ go build -a -gcflags='-S -ssa=0' runtime 2>&1 | grep 'TEXT.*""\.init(SB)'
        0x0000 00000 ($GOROOT/src/runtime/write_err.go:14)        TEXT    "".init(SB), $88-0

With SSA, before this CL:

$ go build -a -gcflags='-S -ssa=1' runtime 2>&1 | grep 'TEXT.*""\.init(SB)'
        0x0000 00000 ($GOROOT/src/runtime/traceback.go:608)       TEXT    "".init(SB), $152-0

With SSA, after this CL:

$ go build -a -gcflags='-S -ssa=1' runtime 2>&1 | grep 'TEXT.*""\.init(SB)'
        0x0000 00000 ($GOROOT/src/runtime/write_err.go:14)        TEXT    "".init(SB), $152-0

Change-Id: Ida3541e03a1af6ffc753ee5c3abeb653459edbf6
Reviewed-on: https://go-review.googlesource.com/20321
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>