multimedia/handbrake: fix build on powerpc64

Use C11 compiler, because of ffmpeg.
Correct comment typo.
Don't include asm/cputable.h and linux/auxvec.h in libvpx-1.7.0/vpx_ports/ppc_cpudetect.c - those headers are Linux-only.
Merge upstream patch from x265 to fix compilation on non-x86.
Don't link with libc++ when using GCC.

PR: 241928
Approved by: naito.yuichiro@gmail.com (maintainer), linimon (mentor)