Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Upgrade our copy of llvm/clang to trunk r162107. With thanks to
Benjamin Kramer and Joerg Sonnenberger for their input and fixes.

adds bwn(4) driver for supporting Broadcom BCM43xx chipsets.

o uses v4 firmware instead of v3. A port will be committed to create
the bwn firmware module.
o supports B/G and LP(low power) PHYs.
o supports 32 / 64 bits DMA operations.
o tested on big / little endian machines so should work on all
architectures.

It'd not connected to the build until the firmware port is committed.