xen/build: Automatically locate a suitable python interpreter
Needing to pass PYTHON=python3 into hypervisor builds is irritating and unnecessary. Locate a suitable interpreter automatically, defaulting to Py3 if it is available. Reported-by: Steven Haigh <netwiz@crc.id.au> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: George Dunlap <George.Dunlap@eu.citrix.com> CC: Ian Jackson <ian.jackson@citrix.com> CC: Jan Beulich <JBeulich@suse.com> CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> CC: Stefano Stabellini <sstabellini@kernel.org> CC: Wei Liu <wl@xen.org> CC: Julien Grall <julien@xen.org> CC: Steven Haigh <netwiz@crc.id.au> CC: Juergen Gross <jgross@suse.com> v2: * Cope with `which` not being present in the system. * Only evaulate the shell command one, rather than once per $(PTHON) usage For 4.13. This is a very-nice-to-have WRT our Py3-clean intention.