Build: Update ARMClang version to 6.18

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I775823cf30b2667652addc96da7d1147262c795f
diff --git a/memory_footprint.py b/memory_footprint.py
index 05c1958..801c0bc 100644
--- a/memory_footprint.py
+++ b/memory_footprint.py
@@ -121,7 +121,7 @@
 
 if __name__ == "__main__":
     # Export ARMClang v6.13 to ENV PATH
-    os.environ["PATH"] += os.pathsep + os.getenv('ARMCLANG_6_13_PATH')
+    os.environ["PATH"] += os.pathsep + os.getenv('ARMCLANG_6_18_PATH')
     if os.getenv('CONFIG_NAME') in reference_configs:
         print("Configuration " + os.getenv('CONFIG_NAME') + " is a reference")
         try :