cmd/cgo: don't let #cgo directives mess up line numbering

Fixes #5272.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/13498046
diff --git a/src/run.bash b/src/run.bash
index 52e09b4..9af3f95 100755
--- a/src/run.bash
+++ b/src/run.bash
@@ -145,6 +145,12 @@
 go run main.go || exit 1
 ) || exit $?
 
+[ "$CGO_ENABLED" != 1 ] ||
+[ "$GOHOSTOS" == windows ] ||
+(xcd ../misc/cgo/errors
+./test.bash || exit 1
+) || exit $?
+
 (xcd ../doc/progs
 time ./run || exit 1
 ) || exit $?