Patch applied to zlib...
Zero errors and zero warnings compiling nginx 1.9.5 with clang/llvm 3.7.0.
Well done...

--- inflate.c.orig 2015-09-23 18:22:54.000000000 +0200
+++ inflate.c 2015-09-23 18:23:45.000000000 +0200
@@ -1504,9 +1504,10 @@
{
struct inflate_state FAR *state;

- if (strm == Z_NULL || strm->state == Z_NULL) return -1L << 16;
+ if (strm == Z_NULL || strm->state == Z_NULL)
+ return (long)(((unsigned long)0 - 1) << 16);
state = (struct inflate_state FAR *)strm->state;
- return ((long)(state->back) << 16) +
+ return (long)(((unsigned long)((long)state->back)) << 16) +
(state->mode == COPY ? state->length :
(state->mode == MATCH ? state->was - state->length : 0));
}