[mips][msa] Update encoding of LDI instruction.

The encoding was updated in MSA r1.07.
Thread the info about vbptr sharing through ASTRecordLayout

Reviewed at http://llvm-reviews.chandlerc.com/D2120
llvm-ar: Let opening a directory failed in llvm-ar.

Linux cannot open directories with open(2), although cygwin and *bsd can.

Motivation: The test, Object/directory.ll, had been failing with --target=cygwin on Linux. XFAIL was improper for host issues.