Support: add Windows ARM EH data structures

Introduce the support structures necessary to deal with the Windows ARM EH data.
These definitions are extremely aggressive about assertions to aid future use
for generation of the entries and subsequent decoding.

The names for the various fields are meant to reflect the names used by the
Visual Studio toolchain to aid communication.

Due to the complexity in reading a few of the values, there are a couple of
additional utility functions to decode the information.

In general, there are two ways to encode the unwinding information:
- packed, which places the data inline into the
  _IMAGE_ARM_RUNTIME_FUNCTION_ENTRY structure.
- unpacked, which places the data into auxiliary structures placed into the
  .xdata section.

The set of structures allow reading of data in either encoding, with the minor
caveat that epilogue scopes need to be decoded manually by constructing the
structure from the data returned by the RuntimeFunction structure.

These definitions are meant for read-only access at the current point as the
first use of them will be to decode the exception information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209998 91177308-0d34-0410-b5e6-96231b3b80d8
Support: add 6-parameter format

Since we cannot yet use variadic templates, add a specialisation for
6-parameters to format.  This is motivated by a need for the additional
parameter for formatting information for an unwind decoder for Windows on ARM.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209999 91177308-0d34-0410-b5e6-96231b3b80d8
Instruction::isIdenticalToWhenDefined(): Check getNumOperands() in advance of std::equal(op) to appease MSVC Debug build.

MSVC Debug build is confused with (possibly invalid) op_begin(), if op_begin() == op_end().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210000 91177308-0d34-0410-b5e6-96231b3b80d8
GraphWriter: detect graph viewer programs at runtime

Replace the crufty build-time configure checks for program paths with
equivalent runtime logic.

This lets users install graphing tools as needed without having to reconfigure
and rebuild LLVM, while eliminating a long chain of inappropriate compile
dependencies that included GUI programs and the windowing system.

Additional features:

 * Support the OS X 'open' command to view graphs generated by any of the
   Graphviz utilities. This is an alternative to the Graphviz OS X UI which is
   no longer available on Mountain Lion.

 * Produce informative log output upon failure to indicate which programs can
   be installed to view graphs.

Ping me if this doesn't work for your particular environment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210001 91177308-0d34-0410-b5e6-96231b3b80d8