[FRONTEND] Fixed inliner and got more tests to pass (#822)

This adds a `DialectInlinerInterface` to the Triton dialect. This, along
with a few other minor semantic changes, fixes our tests on call
instructions. Also added the option to provide use an "LLVM_SYSPATH"
environment variable to link against locally build of LLVM; this was
useful for debugging this issue.

include/triton/Dialect/Triton/Transforms/Passes.h

@@ -8,7 +8,7 @@ namespace triton {
 
 std::unique_ptr<Pass> createCombineOpsPass();
 
-}
+} // namespace triton
 
 #define GEN_PASS_REGISTRATION
 #include "triton/Dialect/Triton/Transforms/Passes.h.inc"