Do not require rdkafka if it is static lib

Author: Nikita Vakula

CMakeLists.txt

@@ -92,6 +92,8 @@ endif()
 
 if (CPPKAFKA_RDKAFKA_STATIC_LIB)
     add_definitions("-DLIBRDKAFKA_STATICLIB")
+else ()
+    set(RDKAFKA_REQUIRES "rdkafka >= 0.9.4")
 endif()
 
 if (NOT CPPKAFKA_CONFIG_DIR)

cmake/cppkafka.pc.in

@@ -9,6 +9,6 @@ Url: https://github.com/mfontanini/cppkafka
 Description: C++ wrapper library on top of RdKafka
 Version: @CPPKAFKA_VERSION@
 Requires:
-Requires.private: rdkafka >= 0.9.4
+Requires.private: @RDKAFKA_REQUIRES@
 Libs: -L${libdir} -L${sharedlibdir} -lcppkafka
 Cflags: -I${includedir} -I${includedir}/cppkafka -I@Boost_INCLUDE_DIRS@