Merge pull request #3711 from yan12125/centos7-static-linking

Fix linking to libzmq.a statically on CentOS 7

RELICENSE/yan12125.md

+# Permission to Relicense under MPLv2
+
+This is a statement by Chih-Hsuan Yen
+that grants permission to relicense its copyrights in the libzmq C++
+library (ZeroMQ) under the Mozilla Public License v2 (MPLv2).
+
+A portion of the commits made by the Github handle "yan12125", with
+commit author "Chih-Hsuan Yen <yan12125@gmail.com>", are copyright of Chih-Hsuan Yen.
+This document hereby grants the libzmq project team to relicense libzmq, 
+including all past, present and future contributions of the author listed above.
+
+Chih-Hsuan Yen
+2019/10/12

src/libzmq.pc.in

@@ -7,6 +7,6 @@ Name: libzmq
 Description: 0MQ c++ library
 Version: @VERSION@
 Libs: -L${libdir} -lzmq
-Libs.private: -lstdc++ @pkg_config_libs_private@
+Libs.private: -lstdc++ -lm @pkg_config_libs_private@
 Requires.private: @pkg_config_names_private@
 Cflags: -I${includedir} @pkg_config_defines@