Compiling with warnings and certain compiler flags is important for security and bug-free code. Set a bunch of warnings via AM_CFLAGS in a common Makefile, and let those values propagate to all other Makefiles. While here, also fix the version string to remove quotes.

libexec is a common path which is understood by autotools, and should be honoured. Patch from Christian "naddy" Weisgerber

This adds the capability to compile got-portable on FreeBSD.

This commit modifies the GoT main branch to be able to compile it under linux.