Fix JSC::ARM64Assembler::LinkRecord::RealTypes
https://bugs.webkit.org/show_bug.cgi?id=135906

Patch by Akos Kiss <akiss@inf.u-szeged.hu> on 2014-08-14
Reviewed by Michael Saboff.

JSC::ARM64Assembler::LinkRecord::RealTypes::m_compareRegister is defined
to occupy 5 bits but JSC::ARM64Assembler::RegisterID needs 6 bits. So,
increase the size of the bit field and also reorganize the struct to
better align with word boundaries.

* assembler/ARM64Assembler.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@172578 268f45cc-cd09-0410-ab3c-d52691b4dbfc