Make libhtml, htmlfmt build.
Thanks to wkj for doing all the hard work.
diff --git a/src/libhtml/utils.c b/src/libhtml/utils.c
index db22bba..32fd70d 100644
--- a/src/libhtml/utils.c
+++ b/src/libhtml/utils.c
@@ -1,4 +1,5 @@
 #include <u.h>
+#include <limits.h>
 #include <libc.h>
 #include <draw.h>
 #include <html.h>