Fix MCJITCAPITest.cpp unit test on Windows.

MCJIT on Windows requires an explicit target triple with "-elf" appended to generate objects in ELF format.  The common test framework was setting up this triple, but it wasn't passed to the C API in the test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181614 91177308-0d34-0410-b5e6-96231b3b80d8