[mips][msa] Build all the tests in little and big endian modes and correct an incorre...

[mips][msa] Build all the tests in little and big endian modes and correct an incorrect test.

Summary:
This patch (correctly) breaks some MSA tests by exposing the cases when
SelectionDAG::getConstant() produces illegal types. These have been temporarily
marked XFAIL and the XFAIL flag will be removed when
SelectionDAG::getConstant() is fixed.

There are three categories of failure:
* Immediate instructions are not selected in one endian mode.
* Immediates used in ldi.[bhwd] must be different according to endianness.
  (this only affects cases where the 'wrong' ldi is used to load the correct
   bitpattern. E.g. (bitcast:v2i64 (build_vector:v4i32 ...)))
* Non-immediate instructions that rely on immediates affected by the
  previous two categories as part of their match pattern.
  For example, the bset match pattern is the vector equivalent of
  'ws | (1 << wt)'.

One test needed correcting to expect different output depending on whether big
or little endian was in use. This test was
test/CodeGen/Mips/msa/basic_operations.ll and experiences the second category
of failure shown above. The little endian version of this test is named
basic_operations_little.ll and will be merged back into basic_operations.ll in
a follow up commit now that FileCheck supports multiple check prefixes.

Reviewers: bkramer, jacksprat, dsanders

Reviewed By: dsanders

CC: llvm-commits
Differential Revision: http://llvm-reviews.chandlerc.com/D1972

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194806 91177308-0d34-0410-b5e6-96231b3b80d8