macos build fails due to two reasons:
1. using build host ar and ranlib tools
2. using uname -r to get kernel version

First issue is fixed by specifying ar and ranlib from toolchain
Second issue is fixed by specifying kernel release major version=5
Using 'uname -r' from build host for cross-compiling is not a good
idea even for Linux build host

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