XFAIL some of the generic CodeGen tests for Hexagon.

test/CodeGen/Generic/2008-02-20-MatchingMem.ll: Test contains inline assembly not supported by Hexagon.

Following tests are XFAILed due to multiple return values which Hexagon doesn't support.

test/CodeGen/Generic/multiple-return-values-cross-block-with-invoke.ll
test/CodeGen/Generic/select-cc.ll
test/CodeGen/Generic/vector.ll