[build] fix SCons pkg-config err handling (fixes #3066)

(thx elchenberg)

x-ref:
  "OSError in SConstruct on Alpine Linux"
  https://redmine.lighttpd.net/issues/3066

SConstruct

@@ -140,6 +140,8 @@ class Autoconf:
 		try:
 			self.conf.env.ParseConfig(*args, **kw)
 			return True
+		except OSError:
+			return False
 		except Exception as e:
 			print(e.message, file=sys.stderr)
 			return False