fix check for zlib

AC_CHECK_LIB was not correctly checking for the presence of zlib.
We use PKG_CHECK_MODULES instead to add -lz to libring_la_LDFLAGS.

Change-Id: Icfffb898030f886aae8c2c82dc5327f923f0f78e
Tuleap: #746
[stepan.salenikovich@savoirfairelinux.com: modified to use PKG_CHECK_MODULES and ZLIB_LIBS variable instead of -lz]
Signed-off: Stepan Salenikovich <stepan.salenikovich@savoirfairelinux.com>

configure.ac

@@ -158,7 +158,6 @@ AC_TYPE_SIZE_T
 AC_HEADER_TIME
 AC_C_VOLATILE
 AC_CHECK_TYPES([ptrdiff_t])
-AC_CHECK_LIB(zlib, zlib)
 
 PKG_PROG_PKG_CONFIG()
 
@@ -238,7 +237,7 @@ AS_IF([test -n "${CONTRIB_DIR}"], [
         export PKG_CONFIG_PATH_CUSTOM
   ])
   export PKG_CONFIG_PATH="${CONTRIB_DIR}/lib/pkgconfig:${CONTRIB_DIR}/lib64/pkgconfig:$PKG_CONFIG_PATH"
-  LDFLAGS="${LDFLAGS} -L${CONTRIB_DIR}/lib -lz"
+  LDFLAGS="${LDFLAGS} -L${CONTRIB_DIR}/lib"
 
   AS_IF([test "${SYS}" = "darwin"], [
     export LD_LIBRARY_PATH="${CONTRIB_DIR}/lib:$LD_LIBRARY_PATH"
@@ -258,6 +257,9 @@ AS_IF([test -d "${TOOLS_DIR}"], [
   export PATH="${TOOLS_DIR}":$PATH
 ])
 
+dnl Check for zlib
+PKG_CHECK_MODULES(ZLIB, zlib,, AC_MSG_ERROR([zlib not found]))
+
 dnl Check for pjproject
 PKG_CHECK_MODULES(PJPROJECT, libpjproject,, AC_MSG_ERROR([Missing pjproject files]))
 

src/Makefile.am

@@ -54,6 +54,7 @@ libring_la_LDFLAGS = \
 		@PORTAUDIO_LIBS@ \
 		@GNUTLS_LIBS@ \
 		@OPENDHT_LIBS@ \
+		@ZLIB_LIBS@ \
 		$(PCRE_LIBS)
 
 if HAVE_OSX