host-compile fails on macos due to several reasons:
1. host-compile Makefile always selected for linux
2. macos host cc (clang) fails due to implicit-function-declaration
3. ar and ranlib tools are hardcoded in softethervpn Makefiles

All three issues are fixed by this patch

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>