Fix generating pkgconfig file

CMakeLists.txt

@@ -108,6 +108,9 @@ install(FILES ${XISF_PUBLIC_HEADERS} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
 install(FILES ${CMAKE_CURRENT_BINARY_DIR}/libxisf.pc DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)
 install(TARGETS XISF LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR})
 
+list(JOIN PC_LIBS_REQUIRE ", " PC_REQUIRE_STR)
+list(TRANSFORM PC_LIBS_REQUIRE PREPEND "-l")
+list(JOIN PC_LIBS_REQUIRE " " PC_LIBS_STR)
 configure_file(libxisf.pc.in libxisf.pc @ONLY)
 
 #testing

libxisf.pc.in

@@ -7,7 +7,7 @@ Name: @PROJECT_NAME@
 Description: @CMAKE_PROJECT_DESCRIPTION@
 URL: @CMAKE_PROJECT_HOMEPAGE_URL@
 Version: @PROJECT_VERSION@
-Requires.private: @PC_LIBS_REQUIRE@
+Requires.private: @PC_REQUIRE_STR@
 Cflags: -I"${includedir}"
 Libs: -L"${libdir}" -lXISF
-Libs.private: -L"${libdir}" @PC_LIBS_REQUIRE@
+Libs.private: -L"${libdir}" @PC_LIBS_STR@