InstCombine: Improvement to check if signed addition overflows.

This patch implements two things:

1. If we know one number is positive and another is negative, we return true as
    signed addition of two opposite signed numbers will never overflow.

2. Implemented TODO : If one of the operands only has one non-zero bit, and if
    the other operand has a known-zero bit in a more significant place than it
    (not including the sign bit) the ripple may go up to and fill the zero, but
    won't change the sign. e.x -  (x & ~4) + 1

We make sure that we are ignoring 0 at MSB.

Patch by Suyog Sarda.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210186 91177308-0d34-0410-b5e6-96231b3b80d8
Support: add additional comment for ARM EH structure

Replicate the fact that ARM::WinEH::RuntimeFunction purposefully does not merge
functions to accommodate raw data access use cases in tools such as readobj.
Pointed out by Renato during post-commit review.

No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210189 91177308-0d34-0410-b5e6-96231b3b80d8
Support: style/documentation cleanup for format

This is purely a documentation/whitespace cleanup for the format support
functions.

The current style does not duplicate the function/class names in the
documentation; conform to this style.

Additionally, there was a large amount of duplication of comments that added no
real value.  Use block comments for the related sets of functions which are used
for type deduction and parameter container classes.

No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210190 91177308-0d34-0410-b5e6-96231b3b80d8
tools: introduce StreamWriter::printBoolean

Add a helper print method to print a boolean value as "Yes" or "No".  This is
intended to be used by the Windows ARM EH printer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210191 91177308-0d34-0410-b5e6-96231b3b80d8
tools: initial implementation of WoA EH decoding

Add support to llvm-readobj to decode Windows ARM Exception Handling data.  This
uses the previously added datastructures to decode the information into a format
that can be used by tests.  This is a necessary step to add support for emitting
Windows on ARM exception handling information.

A fair amount of formatting inspiration is drawn from the Win64 EH printer as
well as the ARM EHABI printer.  This allows for a reasonably thorough look into
the encoded data.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210192 91177308-0d34-0410-b5e6-96231b3b80d8