Specify GCC 11's default C++ version behavior

Author: jakirkham

src/user/announcements.rst

@@ -39,9 +39,9 @@ Our announcements are published to an RSS feed `here <https://conda-forge.org/do
     These compilers will become the default for building packages in conda-forge.
     One notable change in gcc 10 is that the -fopenmp flag in FFLAGS is dropped.
     In clang 12, -std=c++14 explicit flag has been dropped from CXXFLAGS,
-    as it is the default compilation mode for clang 12. In clang>=12 and gcc>=11,
-    we will not provide an explicit C++ standard, and will defer to the compiler
-    default.
+    as it is the default compilation mode for clang 12. In gcc 11, the default
+    is -std=gnu++17. In clang>=12 and gcc>=11, we will not provide an explicit
+    C++ standard, and will defer to the compiler default.
 
 :2021-10-04: python 3.6 is now dropped when building conda-forge packages