Add -std=c11 to Ruby build.

[skrah]

@v0dro I have to use gem install ndtypes --verbose --pre -- --with-cflags="-std=c11" for the build.

Is it possible to integrate -std=c11 in some configuration file?

[v0dro]

Sure. I'll do that.

[v0dro]

It can be done in the extconf.rb file by setting up the CFLAGS variable.