rework Makefile

- 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)

config.mk

@@ -1,13 +1,12 @@
 _VERSION = 0.3.1-dev
 VERSION  = `git describe --long --tags --dirty 2>/dev/null || echo $(_VERSION)`
 
+PKG_CONFIG = pkg-config
+
 # paths
 PREFIX = /usr/local
 MANDIR = $(PREFIX)/share/man
 
-# Compile flags that can be used
-#CFLAGS = -pedantic -Wall -Wextra -Werror -Wno-unused-parameter -Wno-sign-compare -Wno-unused-function -Wno-unused-variable -Wno-unused-result -Wdeclaration-after-statement
-
 XWAYLAND =
 XLIBS =
 # Uncomment to build XWayland support