- allow user to use a different pkg-config binary
- restore almost all (and add other ones) warning flags (-Werror is not set)
- $(XWAYLAND) is added to our CPPFLAGS
- remove useless comments
- don't generate idle-protocol.h (not used)
Similar to Linux kernel approach, encapsulate some of the uglier
conditional compilation into inline functions in header files.
The goal is to make dwl.c more attractive to people who embrace the
suckless philosophy - simple, short, hackable, and easy to understand.
We want dwm users to feel comfortable here, not scare them off. Plus,
if we do this right, the main dwl.c code should require only minimal
changes once XWayland is no longer a necessary evil.
According to `cloc`, this also brings dwl.c down below 2000 lines of
non-blank, non-comment code.
