Building in a tree with read-only source files failed because the flex/
bison generated files are left in place.

All of the source files (instead of all of the object files) were
depending on libxl.h (in particular forcing the needless re-generation
of the flex/bison generated files).

For _libxl_types.[ch] a single non-pattern rule was used. For non-
pattern rules with multiple targets, other than for pattern ones, the
body gets executed once for each target, causing problems when building
with -j<n>, <n> >= 2. Convert this rule to a pattern one.

The flex/bison generated headers pointlessly depended on the
corresponding source files. Use multiple-target pattern rules instead.

It would also have been nice if the minimal flex/bison versions needed
to successfully build libxl were documented: neither flex 2.5.31 nor
bison 2.1 (as found e.g. on SLE10) is sufficient.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- 2010-09-20.orig/tools/libxl/Makefile	2010-09-20 14:23:28.000000000 +0200
+++ 2010-09-20/tools/libxl/Makefile	2010-09-20 14:24:20.000000000 +0200
@@ -42,18 +42,15 @@ XL_OBJS = xl.o xl_cmdimpl.o xl_cmdtable.
 all: $(CLIENTS) libxenlight.so libxenlight.a libxlutil.so libxlutil.a \
 	$(AUTOSRCS) $(AUTOINCS)
 
-$(AUTOINCS): $(AUTOSRCS)
-
-#%_y.h: %_y.c
-#%_l.h: %_l.c
-
 $(LIBXLU_OBJS): $(AUTOINCS)
 
-%.c: %.y
-	$(BISON) --output=$@ $<
-
-%.c: %.l
-	$(FLEX) --header-file=$*.h --outfile=$@ $<
+%.c %.h: %.y
+	@rm -f $*.[ch]
+	$(BISON) --output=$*.c $<
+
+%.c %.h: %.l
+	@rm -f $*.[ch]
+	$(FLEX) --header-file=$*.h --outfile=$*.c $<
 
 genpath-target = $(call buildmakevars2file,_libxl_paths.h)
 $(eval $(genpath-target))
@@ -66,12 +63,12 @@ libxl_paths.c: _libxl_paths.h
 
 libxl.h: _libxl_types.h
 
-$(LIBXL_OBJS:%.o=%.c) $(LIBXLU_OBJS:%.o=%.c) $(XL_OBJS:%.o=%.c): libxl.h
+$(LIBXL_OBJS) $(LIBXLU_OBJS) $(XL_OBJS): libxl.h
 
-_libxl_types.h _libxl_types.c: libxl.idl gentypes.py libxltypes.py
-	$(PYTHON) gentypes.py libxl.idl __libxl_types.h __libxl_types.c
-	mv __libxl_types.h _libxl_types.h
-	mv __libxl_types.c _libxl_types.c
+_libxl_%.h _libxl_%.c: libxl.idl gen%.py libxl%.py
+	$(PYTHON) gen$*.py libxl.idl __libxl_$*.h __libxl_$*.c
+	mv __libxl_$*.h _libxl_$*.h
+	mv __libxl_$*.c _libxl_$*.c
 
 libxenlight.so: libxenlight.so.$(MAJOR)
 	ln -sf $< $@