Merge branch 'develop'
Updated submodule pointers after merging develop -> master (6.7.0).
Remove prebuilt submodule for merge readiness.
Merge branch 'develop'

Conflicts:
	ide
	thirdparty
[[ Bugfix 13580 ]] Use g++ as compiler by default
[[ Bugfix 13580 ]] Slightly different approach
[[ Bugfix 13580 ]] Just use C++ compiler for engine compilation
[[ Bugfix 13580 ]] Remove various explicit mentions of libstdc++
Merge 'runrevfraser/bugfix-13580' into feature-stackdir.

Needed to fix building on non-Ubuntu x86-64 Linux systems.