Some powerpc-specific code has been borrowed from emulators/qemu and
as such rely on _CALL_* defines that clang does not provide.
Redefine _CALL_SYSV similarly.
OK jasper@ (maintainer), jca@
QEMU's configure script cannot cope with modern Python, but unicorn does.
Pass python2 to QEMU in both cases, otherwise unicorn behaves like any
other flavored python port.
"go ahead" jasper