Index: boot/Makefile.build
===================================================================
--- boot/Makefile.build	(revision 042fbe0c7c1554d67557bfe39825352d0ac29fbe)
+++ boot/Makefile.build	(revision fa7aa509268e6b04611868192a34ad6171310256)
@@ -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