lib9: gcc-4.2 bug in sprint

src/lib9/fmt/sprint.c

diff --git a/src/lib9/fmt/sprint.c b/src/lib9/fmt/sprint.c
index 9e3cb63..4155d88 100644
--- a/src/lib9/fmt/sprint.c
+++ b/src/lib9/fmt/sprint.c
@@ -16,8 +16,11 @@
 	/*
 	 * on PowerPC, the stack is near the top of memory, so
 	 * we must be sure not to overflow a 32-bit pointer.
+	 *
+	 * careful!  gcc-4.2 assumes buf+len < buf can never be true and
+	 * optimizes the test away.  casting to uintptr works around this bug.
 	 */
-	if(buf+len < buf)
+	if((uintptr)buf+len < (uintptr)buf)
 		len = -(uintptr)buf-1;
 
 	va_start(args, fmt);