package/Makefile.in: remove HOSTCC_VERSION

HOSTCC_VERSION is no longer used since gcc switched to the package
infrastructure in e236fe48. It was in fact no longer needed since we
dropped support for gcc 4.3.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>