Building native extensions fails when CMAKE_GENERATOR is non-default

[Sharparam]

The extconf.rb file seems to be hardcoded to use gmake or make under Linux environments. This will fail when a different generator is used, like CMAKE_GENERATOR=Ninja.

CMake projects should use cmake --build to build, which makes CMake automatically use the correct build tool.

(Alternatively, if your project must use a specific kind of build system, you need to override it with the -G parameter when generating the build files.)

As a workaround to install the gem, one can run this:

CMAKE_GENERATOR= gem install rugged