Build fix for gcc-15

Author: mikrosk

buildrules

@@ -130,6 +130,7 @@ CFLAGS-crypt = -O3 -fexpensive-optimizations
 # This is necessary to avoid optimizing the sequence of malloc/memset
 # to a call to calloc in its own implementation
 CFLAGS-calloc.c = -fno-builtin
+CFLAGS-syscall.c = -std=gnu11
 # These source come from ... you know where
 DEFS-xbootparam_prot.c = -Wno-unused
 DEFS-xmount.c = -Wno-unused