Add support for some extended push instructions in i386/x86_64 like

'push 0x20(%esp)' which clang can generate when emitting
-fomit-frame-pointer code for 32-bit.

Add a unit test program which includes this instruction.

Also fix a bug in the refactoring/rewrite of the x86 assembly
instruction profiler where I'd hard coded it as a 64-bit disassembler
instead of using the ArchSpec to pick a 32-bit or 64-bit disassembler
from llvm.  When the disassembler would hit an instruction
that is invalid in 64-bit mode, it would stop disassembling the function.
This likely led to the TestSBData testsuite failure on linux with 32-bit
i386 and gcc-4.9; I'll test that in a bit.

The newly added unit test program is 32-bit i386 code and it includes
an instruction which is invalid in 64-bit mode so it will catch this.

<rdar://problem/28557876> 

llvm-svn: 282991