MFH: r546865
games/megaglest: fix build with LLVM 11
The fallout here is due to the new -fno-common default in GCC 10 / LLVM 11.
PR: 248870
Obtained from: https://github.com/MegaGlest/megaglest-source/issues/197
Approved by: ports-secteam (-fno-common build fix)