Removed GNU make constructs from Makefile.

Prepared for repair of "make distcheck".

atom/Makefile.am

@@ -7,21 +7,21 @@ xcbinclude_HEADERS = xcb_atom.h
 
 AM_CFLAGS = -Wall
 
-libXCBAtom_la_SOURCES = atoms.c
+libXCBAtom_la_SOURCES = atoms.c atomlist.m4 atoms.gperf.m4 xcb_atom.h.m4
 libXCBAtom_la_CFLAGS = $(XCB_CFLAGS)
 libXCBAtom_la_LIBADD = $(XCB_LIBS)
 
 pkgconfig_DATA = xcb-atom.pc
 
-EXTRA_DIST = xcb-atom.pc.in atomlist.m4 atoms.gperf.m4 xcb_atom.h.m4
+EXTRA_DIST = xcb-atom.pc.in
 
 BUILT_SOURCES = atoms.c atoms.gperf xcb_atom.h
 
-%.c: %.gperf
-	$(GPERF) --output-file $@ $*.gperf
+atoms.c: atoms.gperf
+	$(GPERF) --output-file $@ $<
 
-atoms.gperf: atomlist.m4
-xcb_atom.h: atomlist.m4
+atoms.gperf: atoms.gperf.m4 atomlist.m4
+	$(M4) $< >$@
 
-%: %.m4
-	$(M4) $< > $@
+xcb_atom.h: xcb_atom.h.m4 atomlist.m4
+	$(M4) $< >$@