intercept puts() in libsys, for gcc

lib/libsys/Makefile

@@ -98,6 +98,7 @@ SRCS=  \
 	asynsend.c \
 	kprintf.c \
 	kputc.c \
+	kputs.c \
 	tickdelay.c \
 	get_randomness.c \
 	getidle.c \

lib/libsys/kputs.c

@@ -0,0 +1,24 @@
+/* system services puts()
+ *
+ * This is here because gcc converts printf() calls without actual formatting
+ * in the format string, to puts() calls. While that "feature" can be disabled
+ * with the -fno-builtin-printf gcc flag, we still don't want the resulting
+ * mayhem to occur in system servers even when that flag is forgotten.
+ */
+
+#include <stdio.h>
+
+/* puts() uses kputc() to print characters. */
+void kputc(int c);
+
+int puts(const char *s)
+{
+
+	for (; *s; s++)
+		kputc(*s);
+
+	kputc('\n');
+	kputc('\0');
+
+	return 0;
+}