Add "Libs.private: -m" to wolfssl.pc.in for a static linking

Author: mpsuzuki

support/wolfssl.pc.in

@@ -7,4 +7,5 @@ Name: wolfssl
 Description: wolfssl C library.
 Version: @VERSION@
 Libs: -L${libdir} -lwolfssl
+Libs.private: -lm
 Cflags: -I${includedir}