DeviceGL Compile Error On Linux.

[wzhengsen]

• cocos2d-x version:
  Engine-X

• devices test on:
  Ubuntu 20.04.1 LTS

• developing environments
  GCC for x86_64-linux-gnu 9.30

• file:
  DeviceGL.cpp-line 101

[halx99]

Pease tack the pr: #217

[halx99]

see also: https://travis-ci.com/github/c4games/engine-x/builds/186413112

build requirement:

• ubuntu-18.04+
• glibc-2.27+
• New dependency: libbsd-dev: sudo apt-get install libbsd-dev