Merge in updates for mipsn32 and 32-bit arm.

[jhb]

Summary

• Brings in upstream commits to fix debugging on mipsn32 (properly parsing registers and signal information in core dumps as well as unwinding across signal frames)
• Brings in reworked ARM support. Portions of this (support for new AT_* values and NT_ARM_VFP core dump note) are already upstreamed, but the main FreeBSD arm bits are still pending review. Compared to the existing patch-armfbsd, these versions include generic FreeBSD target support (auxv, thread names from cores, $_siginfo, syscall names, etc.) as well as VFP support and an unwinder for signal frames.

Test Plan

• Tested GDB on a RPI 2 with some simple test programs.
• Tested GDB in a mipsn32 qemu instance with some simple test programs.

[jhb]

• Use older regcache functions for 8.0.1.

[pizzamig]

Built on i386 and amd64 on all supported FreeBSD version
Passed my test suite