Fix build on BSD systems

[valpackett]

I guess there might be a better way to run the same make that create_makefile runs?? But this will do.

[lfittl]

@myfreeweb Thanks for the contribution!

For clarification, this make invocation isn't for the Makefile thats generated by extconf itself, but rather for building a C language library the gem depends on for parsing.

Since I don't have FreeBSD readily available for testing, just to confirm, this works correctly on your machine?

[valpackett]

Yeah. The makefile that's generated by extconf works fine (it's either compatible with BSD make, or executed by gmake). The makefile of the library requires GNU make, so gmake needs to be run instead of make. It works fine on my machine, yes.

[lfittl]

@myfreeweb Excellent, thanks for confirming - merged!