hack to unbreak check-llvm on win after https://reviews.llvm.org/D97335

fix attempt http://reviews.llvm.org/rGbbdb4c8c9bcef0e didn't work

The problem is that the test tries to look up
llvm_orc_registerJITLoaderGDBWrapper from the llvm-jitlink.exe
executable, but the symbol wasn't exported. Just manually export it
for now. There's a FIXME with a suggestion for a real fix.