libs/stat: Fix and rework python-bindings build

libs/stat: Fix and rework python-bindings build

Fix the dependency on the library, $(SHLIB) variable doesn't exist
anymore.

Rework dependency on the include file, we can let `swig` generate the
dependency for us with the use of "-M*" flags.

The xenstat.h file has moved so we need to fix the include location.

Rather than relaying on the VCS to create an empty directory for us,
we can create one before generating the *.c file for the bindings.

Make use of generic variable names to build a shared library from a
source file: CFLAGS, LDFLAGS, and LDLIBS.

Fix python's specific *flags by using python-config, and add them to
generic flags variables: CFLAGS, LDLIBS.

To build a shared library, we need to build the source file with
"-fPIC", which was drop by 6d0ec05390 (tools: split libxenstat into
new tools/libs/stat directory).

The source file generated by swig seems to be missing a prototype for
the "init" function, so we need "-Wno-missing-prototypes" in order to
build it.

Add some targets to .PHONY.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>