games/assaultcube: unbreak on DragonFly and the package cluster

• Disable PCH (precompiled header) to unbreak build with GCC in jails for older branches and recent 11.0C kernel
• Add upstream patch for bundled libenet to unbreak build on DragonFly [1]
• Convert patch for ${BUILD_WRKSRC}/Makefile into sed(1) variant
• Pet portlint since r383894 by formatting patches with makepatch target

PR: 199912
Submitted by: lightside <lightside@gmx.com> (maintainer)
Obtained from: https://github.com/lsalzman/enet/commit/8df6e58 [1]