Object: Add support for bigobj

This adds support for reading the "bigobj" variant of COFF produced by
cl's /bigobj and mingw's -mbig-obj.

The most significant difference that bigobj brings is more than 2**16
sections to COFF.

bigobj brings a few interesting differences with it:
- It doesn't have a Characteristics field in the file header.
- It doesn't have a SizeOfOptionalHeader field in the file header (it's
  only used in executable files).
- Auxiliary symbol records have the same width as a symbol table entry.
  Since symbol table entries are bigger, so are auxiliary symbol
  records.

Write support will come soon.

Differential Revision: http://reviews.llvm.org/D5259

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217496 91177308-0d34-0410-b5e6-96231b3b80d8
ARM: don't size-reduce STMs using the LR register.

The only Thumb-1 multi-store capable of using LR is the PUSH instruction, which
translates to STMDB, so we shouldn't convert STMIAs.

Patch by Sergey Dmitrouk.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217498 91177308-0d34-0410-b5e6-96231b3b80d8
Attempt to pacify buildbots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217499 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing HWEncoding to base register class.

This change gives tblgen the information needed to fill in the
HexagonRegEncodingTable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217500 91177308-0d34-0410-b5e6-96231b3b80d8