Merge pull request #3714 from mdionisio/remove_libm

Revert "Problem: pkg-config file cannot be used for static linking on…

src/libzmq.pc.in

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