Index: boot/Makefile.build
===================================================================
--- boot/Makefile.build	(revision 042fbe0c7c1554d67557bfe39825352d0ac29fbe)
+++ boot/Makefile.build	(revision e8c5c116302f5f37cbb1f2d23a2b292a146beb49)
@@ -40,5 +40,5 @@
 	-finput-charset=UTF-8 -ffreestanding -fno-builtin -nostdlib -nostdinc \
 	-Wall -Wextra -Wno-unused-parameter -Wmissing-prototypes \
-	-Werror-implicit-function-declaration -Wwrite-strings \
+	-std=gnu99 -Werror-implicit-function-declaration -Wwrite-strings \
 	-pipe