[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.

lib/Dialect/Triton/IR/Dialect.cpp

@@ -8,11 +8,30 @@
 
 #include "mlir/IR/DialectImplementation.h"
 
+#include "mlir/Transforms/InliningUtils.h"
 #include "triton/Dialect/Triton/IR/Dialect.cpp.inc"
 
 using namespace mlir;
 using namespace mlir::triton;
 
+//===----------------------------------------------------------------------===//
+// TritonDialect Dialect Interfaces
+//===----------------------------------------------------------------------===//
+
+namespace {
+struct TritonInlinerInterface : public DialectInlinerInterface {
+  using DialectInlinerInterface::DialectInlinerInterface;
+  bool isLegalToInline(Region *dest, Region *src, bool wouldBeCloned,
+                       BlockAndValueMapping &valueMapping) const final {
+    return true;
+  }
+  bool isLegalToInline(Operation *, Region *, bool wouldBeCloned,
+                       BlockAndValueMapping &) const final {
+    return true;
+  }
+};
+} // namespace
+
 void TritonDialect::initialize() {
   registerTypes();
 
@@ -22,6 +41,7 @@ void TritonDialect::initialize() {
       >();
 
   // We can also add interface here.
+  addInterfaces<TritonInlinerInterface>();
 }
 
 Operation *TritonDialect::materializeConstant(OpBuilder &builder,