Adapted from https://mirrors.slackware.com/slackware/slackware-current/source/a/lilo/lilo.gcc15.diff
--- a/make.vars
+++ b/make.vars
@@ -80,7 +80,7 @@
 MAN_DIR=/usr/share/man
 
 # set the compiler optimization level
-OPT=-Os
+OPT=-Os -std=gnu17
 
 ### End of configuration variables for makefiles ###