Use C++17 by default in aiecc

Otherwise it creates a lot of warning with XRT which uses (7-year old) C++17.

python/compiler/aiecc/main.py

@@ -659,7 +659,7 @@ async def process_host_cgen(self, aie_target, file_with_addresses):
                     ],
                 )
 
-            cmd = ["clang++", "-std=c++11"]
+            cmd = ["clang++", "-std=c++17"]
             if opts.host_target:
                 cmd += ["--target=" + opts.host_target]
                 if (