[AMD] support reading hip lld path from env variables (intel#3917)

When compiling AMD Triton kernels on non-AMD GPU machines, we didn't
have either "/opt/rocm/llvm/bin/ld.lld" or "/usr/bin/ld.lld" paths. In
such case, introduce an `TRITON_HIP_LLD_PATH` env variable to a
third-party path. We had such support in the forked version. This PR
added the support to the upstream version.

Author: sijiac

third_party/amd/backend/compiler.py

@@ -85,7 +85,13 @@ def load_dialects(self, ctx):
 
     @staticmethod
     def path_to_rocm_lld():
-        # First check backend for ld.lld (used for pytorch wheels)
+        # Check env path for ld.lld
+        lld_env_path = os.getenv("TRITON_HIP_LLD_PATH")
+        if lld_env_path is not None:
+            lld = Path(lld_env_path)
+            if lld.is_file():
+                return lld
+        # Check backend for ld.lld (used for pytorch wheels)
         lld = Path(__file__).parent / "llvm/bin/ld.lld"
         if lld.is_file():
             return lld