Norbert Lange authored Jul 26, 2017 and Brad King committed Aug 03, 2017

Set the variable added by commit a2112257 (Add infrastructure to use
language extensions without any standard, 2017-06-29) for IAR.  This was
accidentally left out of commit d8e6cd9e (IAR: Improve support for IAR
ARM Compiler, 2017-06-15).