Binutils/gas/ld port for RISC-V [PATCH v2]

[Palmer Dabbelt <palmer at dabbelt dot com>]

Thanks to everyone who provided feedback for the RISC-V port.  While there are
a few things left to do on our end, I'd like to submit a v2 of the patch set
just so we're all on the same page.  The exact commit I'm sending is availiable
here:

  https://github.com/riscv/riscv-binutils-gdb/commit/7d581168c2821edbb503121846530a5b02787fe5

while the branch that I've build things on, which should only contain the
referenced commit and some autogenerated files, is here:

  https://github.com/riscv/riscv-binutils-gdb/tree/riscv-for-upstream-v2

Here's what I think is left to do before we can start to get things upstream:

 * gdb review.  The first two patches are being sent to gdb-patches@sourceware.org.

 * riscv-opc.h is autogenerated from a Python script.  We will either clean up
   this script enough to be suitable for submission, or will write some CPP
   that produces a similar result.

 * I forgot to fix copyright dates, but I've already made it this far into the
   email...  The plan is to only extend copyrights, and mark every committed
   file as changed in 2016 if it's not already.

Additionally, there are a few issues on our github that are relevant, but I'm
not sure if they block upstreaming:

 * https://github.com/riscv/riscv-gnu-toolchain/issues/124 : "sizeof(long
   double)" is 64-bit on RISC-V, which precludes the use of the Q extension for
   128-bit floating point.  This may cause an ABI-breakage.

 * https://github.com/riscv/riscv-gnu-toolchain/pull/136 : The path for ld.so
   might change.  This would definately be an ABI change.

Thanks for all the feedback!

[PATCH 1/7] RISC-V GDB Port
[PATCH 2/7] RISC-V GDB Simulator Port
[PATCH 3/7] RISC-V BFD Port
[PATCH 4/7] RISC-V Binutils Port
[PATCH 5/7] RISC-V GAS Port
[PATCH 6/7] RISC-V LD Port
[PATCH 7/7] RISC-V Opcodes Port