removing syscall when develop under appengine (#745)

This change add possibility to build lib/pq under appengine development
server where syscall is not allowed.

Co-authored-by: Benjamin Ernst <b.ernst@envisia.de>

Author: ernstbe

notify.go

@@ -1,8 +1,5 @@
 package pq
 
-// Package pq is a pure Go Postgres driver for the database/sql package.
-// This module contains support for Postgres LISTEN/NOTIFY.
-
 import (
 	"context"
 	"database/sql/driver"

user_other.go

@@ -1,6 +1,4 @@
-// Package pq is a pure Go Postgres driver for the database/sql package.
-
-//go:build js || android || hurd || zos || wasip1
+//go:build js || android || hurd || zos || wasip1 || appengine
 
 package pq
 

user_posix.go

@@ -1,6 +1,4 @@
-// Package pq is a pure Go Postgres driver for the database/sql package.
-
-//go:build aix || darwin || dragonfly || freebsd || (linux && !android) || nacl || netbsd || openbsd || plan9 || solaris || rumprun || illumos
+//go:build aix || darwin || dragonfly || freebsd || (linux && !android && !appengine) || nacl || netbsd || openbsd || plan9 || solaris || rumprun || illumos
 
 package pq
 

user_windows.go

@@ -1,4 +1,5 @@
-// Package pq is a pure Go Postgres driver for the database/sql package.
+//go:build windows && !appengine
+
 package pq
 
 import (