update llvm build script

build-scripts/build_llvm.py

@@ -102,18 +102,26 @@ def build_llvm(llvm_dir, platform, backends, projects, use_clang=False, extra_fl
         "default": [],
     }
 
-    normal_backends = [s for s in backends if s != "ARC"]
-    expeirmental_backends = [s for s in backends if s == "ARC"]
+    normal_backends = [s for s in backends if s != "ARC" and s != "Xtensa"]
+    experimental_backends = [s for s in backends if s == "ARC" or s == "Xtensa"]
 
     LLVM_TARGETS_TO_BUILD = [
         '-DLLVM_TARGETS_TO_BUILD:STRING="' + ";".join(normal_backends) + '"'
         if normal_backends
         else '-DLLVM_TARGETS_TO_BUILD:STRING="AArch64;ARM;Mips;RISCV;X86"'
     ]
 
-    # if not on ARC platform, but want to add expeirmental backend ARC as target
-    if platform != expeirmental_backend:
-        LLVM_TARGETS_TO_BUILD.extend(LLVM_EXTRA_COMPILE_OPTIONS[expeirmental_backend.lower()])
+    for experimental_backend in experimental_backends:
+        # if not on ARC platform, but want to add expeirmental backend ARC as target
+        if platform != "ARC" and experimental_backend == "ARC":
+            LLVM_TARGETS_TO_BUILD.extend(
+                LLVM_EXTRA_COMPILE_OPTIONS[experimental_backend.lower()]
+            )
+        elif platform != "Xtensa" and experimental_backend == "Xtensa":
+            print(
+                "Currently it's not supported to build Xtensa backend on non-Xtensa platform"
+            )
+            return None
 
     LLVM_PROJECTS_TO_BUILD = [
         '-DLLVM_ENABLE_PROJECTS:STRING="' + ";".join(projects) + '"' if projects else ""
@@ -275,6 +283,10 @@ def main():
     )
     options = parser.parse_args()
 
+    # Ensure options.arch is always a list
+    if options.arch is None:
+        options.arch = []
+
     # if the "platform" is not identified in the command line option,
     # detect it
     if not options.platform: