Bug#1060885: gambc: Please add loongarch support

[wuruilong]

Source: gambc
Version: 4.9.3-1.3
Followup-For: Bug #1060885
X-Debbugs-Cc: wuruil...@loongson.cn

Dear Maintainer,

I verified that the above patch compiles successfully on the loongarch 
platform, please merge the attached patch.

wuruilong