Update comment to mention IAR

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/common.h b/library/common.h
index 49f457c..0c5e1e1 100644
--- a/library/common.h
+++ b/library/common.h
@@ -327,7 +327,7 @@
 /* clang provides __builtin_assume */
 #define MBEDTLS_ASSUME(x)       __builtin_assume(x)
 #elif MBEDTLS_HAS_BUILTIN(__builtin_unreachable)
-/* gcc can use __builtin_unreachable */
+/* gcc and IAR can use __builtin_unreachable */
 #define MBEDTLS_ASSUME(x)       do { if (!(x)) __builtin_unreachable(); } while (0)
 #elif defined(_MSC_VER)
 /* Supported by MSVC since VS 2005 */