BUILD: use inttypes.h instead of stdint.h

I found on an (old) AIX 5.1 machine that stdint.h didn't exist while
inttypes.h which is expected to include it does exist and provides the
desired functionalities.

As explained here, stdint being just a subset of inttypes for use in
freestanding environments, it's probably always OK to switch to inttypes
instead:

  https://pubs.opengroup.org/onlinepubs/009696799/basedefs/stdint.h.html

Also it's even clearer here in the autoconf doc :

  https://www.gnu.org/software/autoconf/manual/autoconf-2.61/html_node/Header-Portability.html

  "The C99 standard says that inttypes.h includes stdint.h, so there's
   no need to include stdint.h separately in a standard environment.
   Some implementations have inttypes.h but not stdint.h (e.g., Solaris
   7), but we don't know of any implementation that has stdint.h but not
   inttypes.h"
diff --git a/include/common/http-hdr.h b/include/common/http-hdr.h
index 8cc7ee7..ffca828 100644
--- a/include/common/http-hdr.h
+++ b/include/common/http-hdr.h
@@ -27,7 +27,7 @@
 #ifndef _COMMON_HTTP_HDR_H
 #define _COMMON_HTTP_HDR_H
 
-#include <stdint.h>
+#include <inttypes.h>
 #include <common/ist.h>
 
 /* a header field made of a name and a value. Such structure stores 4 longs so