Fix option append

Author: emilmont

workspace_tools/toolchains/gcc.py

@@ -38,7 +38,7 @@ def __init__(self, target, options=None, notify=None, tool_path=""):
             ] + self.cpu
 
         if "save-asm" in self.options:
-            common_flags.extends("-save-temps")
+            common_flags.append("-save-temps")
 
         self.asm = [join(tool_path, "arm-none-eabi-as")] + self.cpu