Re #2059 (misc): Fixed possible function name clash with md5 due to non-static function.

Backported from: https://trac.pjsip.org/repos/changeset/5688
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>

Index: pjlib-util/src/pjlib-util/md5.c
===================================================================
diff --git a/pjproject/pjlib-util/src/pjlib-util/md5.c b/pjproject/pjlib-util/src/pjlib-util/md5.c
--- a/pjlib-util/src/pjlib-util/md5.c	(revision 5687)
+++ b/pjlib-util/src/pjlib-util/md5.c	(revision 5688)
@@ -29,13 +29,13 @@
 #ifndef HIGHFIRST
 #define byteReverse(buf, len)	/* Nothing */
 #else
-void byteReverse(unsigned char *buf, unsigned longs);
+static void byteReverse(unsigned char *buf, unsigned longs);
 
 #ifndef ASM_MD5
 /*
  * Note: this code is harmless on little-endian machines.
  */
-void byteReverse(unsigned char *buf, unsigned longs)
+static void byteReverse(unsigned char *buf, unsigned longs)
 {
     pj_uint32_t t;
     do {