audio/py-webrtcvad: fix build with GCC-based architectures

GCC architectures need USES=compiler:c11 for BYTE_ORDER compiler macro.

They also need a patch to properly define WEBRTC_ARCH_BIG_ENDIAN.

PR: 237876
Approved by: tcberner (mentor), yuri (maintainer)
Differential Revision: https://reviews.freebsd.org/D20440