check if libdl and libz are really needed

[pabuhler]

    In this case |I found that it was mileading mesage. If you will look closet on the bottom openssl detection

libsrtp/configure.ac

Lines 208 to 256 in cc362ae

	AC_ARG_ENABLE([openssl],
	[AS_HELP_STRING([--enable-openssl], [compile in OpenSSL crypto engine])],
	[], [enable_openssl=no])
	AC_MSG_RESULT([$enable_openssl])
	AC_MSG_CHECKING([whether to leverage NSS crypto])
	AC_ARG_ENABLE([nss],
	[AS_HELP_STRING([--enable-nss], [compile in NSS crypto engine])],
	[], [enable_nss=no])
	AC_MSG_RESULT([$enable_nss])
	if test "$enable_openssl" = "yes"; then
	AC_MSG_CHECKING([for user specified OpenSSL directory])
	AC_ARG_WITH([openssl-dir],
	[AS_HELP_STRING([--with-openssl-dir], [Location of OpenSSL installation])],
	[if test "x$PKG_CONFIG" != "x" && test -f $with_openssl_dir/lib/pkgconfig/libcrypto.pc; then
	if test "x$PKG_CONFIG_PATH" = "x"; then
	export PKG_CONFIG_PATH="$with_openssl_dir/lib/pkgconfig"
	else
	export PKG_CONFIG_PATH="$with_openssl_dir/lib/pkgconfig:$PKG_CONFIG_PATH"
	fi
	AC_MSG_RESULT([$with_openssl_dir])
	elif test -d $with_openssl_dir/lib; then
	CFLAGS="$CFLAGS -I$with_openssl_dir/include"
	if test "x$LDFLAGS" = "x"; then
	LDFLAGS="-L$with_openssl_dir/lib"
	else
	LDFLAGS="$LDFLAGS -L$with_openssl_dir/lib"
	fi
	AC_MSG_RESULT([$with_openssl_dir])
	else
	AC_MSG_RESULT([invalid])
	AC_MSG_FAILURE([Invalid OpenSSL location: $with_openssl_dir])
	fi],
	[AC_MSG_RESULT([no])])
	if test "x$PKG_CONFIG" != "x"; then
	PKG_CHECK_MODULES([crypto], [libcrypto >= 1.0.2i],
	[CFLAGS="$CFLAGS $crypto_CFLAGS"
	LIBS="$crypto_LIBS $LIBS"
	openssl_cleanse_broken=no],
	[PKG_CHECK_MODULES([crypto], [libcrypto >= 1.0.1],
	[CFLAGS="$CFLAGS $crypto_CFLAGS"
	LIBS="$crypto_LIBS $LIBS"
	openssl_cleanse_broken=maybe])])
	else
	AC_CHECK_LIB([dl], [dlopen], [], [AC_MSG_WARN([can't find libdl])])
	AC_CHECK_LIB([z], [inflate], [], [AC_MSG_WARN([can't find libz])])
	fi

you can fiund libdl and libz detections.
I had no installed libz devel resources and that message was printed by incorrecvt logic in tjhat section
Looks like libz detection can be removed because nothing in source tree is usimg libz.

[tkloczko@devel-g2v libsrtp-2.4.2]$ grep zlib.h -r
[tkloczko@devel-g2v libsrtp-2.4.2]$

Whole section could be dramatically reduced if PKG_CHECK_MODULES() aclocal macro would be used.

Originally posted by @kloczek in #599 (comment)

[pabuhler]

Follow up on @kloczek 's comments in #599