kbuild: Don't mandate gcc as the host compiler

Systems that use clang may not have gcc installed.  Set
HOSTCC to cc and HOSTCXX to c++ like we did before to make those
systems work again.

Fixes: 5f520875bdf0 ("kbuild: Bump the build system to 5.1")
Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
1 file changed