[gmime] Check for zlib.h in configure.ac

[Jeffrey Stedfast <fejj src gnome org>]

commit 30d2e32ad0a01e298816d83704424091c9fd708a
Author: Jeffrey Stedfast <jestedfa microsoft com>
Date:   Fri Dec 9 11:52:09 2016 -0500

    Check for zlib.h in configure.ac

 configure.ac |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index e0fef60..8a70688 100644
--- a/configure.ac
+++ b/configure.ac
@@ -162,6 +162,7 @@ AC_CHECK_HEADERS(netdb.h)
 AC_CHECK_HEADERS(regex.h)
 AC_CHECK_HEADERS(time.h)
 AC_CHECK_HEADERS(poll.h)
+AC_CHECK_HEADERS(zlib.h)
 
 AC_TYPE_OFF_T
 AC_TYPE_SIZE_T