August 18th Toolchain Release

It's been about two months singe the last stable toolchain release, so
we're a bit past new on a new one. Here's a summary of the changes
since the June release:

binutils/gdb:

• Now based on the 2.29 upstream release.
• 5852e73c72db RISC-V: Support PCREL_* relocations agaist weak
  undefined symbols
• 0419befe6f92 (WIP) RISC-V: Provide better disassembly of alignment
  sequences
• 160ba91886e3 (WIP) objdump: Provide the found reloc to the disassembler
• 779cd1f46451 (WIP) RISC-V: Avoid emitting invalid instructions in mixed
  RVC/no-RVC code
• ceef952725fb (WIP) RISC-V: Print an error when unable to align a section

We're not including GCC 7.2 here as it's just a bit too new, so there
are no changes to our GCC port.

May 3rd 2017 Toolchain Release

As you may have noticed, we recently had an upstream release of GCC that
contains RISC-V support. Since we're now upstream in binutils and GCC it seems
like a good time to start tagging releases of riscv-gnu-toolchain as stable.
I've tagged the current release on github. Since this is a sort of meta-repo,
I thought the best versioning scheme would just be the current date, so that's
what I'm going with.

I'll try to regularly tag stable releases of the toolchain. I'm going to just
play it by ear as to how frequently I release these, but I anticipate it being
between weekly and monthly. All these tagged release will have passed the
various test suites we run, and I'll write a change log on all the future
releases so users don't have to track commits.

Note that just because we've tagged a release doesn't mean things are stable:
glibc and Linux still aren't upstream so their ABIs aren't set in stone yet
(though we hope not to have to change them). I'm checking the "This is a
pre-release" button on GitHib due to possibility of ABI changes.