check for nasm dependency in the next x264 update

To whoever does the next x264 update: please be aware that they've just switched from yasm to nasm in order to support AVX-512 instructions in *master* branch: https://git.videolan.org/?p=x264.git;a=commit;h=d2b5f4873e2147452a723b61b... x86: Change assembler from yasm to nasm I'm not sure when this will be merged into *stable* branch that we're tracking currently, but it's worth keeping an eye on in order to avoid building without asm support unexpectedly. Regards, Dominik -- Fedora http://fedoraproject.org/wiki/User:Rathann RPMFusion http://rpmfusion.org "Faith manages." -- Delenn to Lennier in Babylon 5:"Confessions and Lamentations"