Tests run against static library (upstream build system):
We build main as both shared & static, main10 & 12 are static only and linked into main.
All need PLATFORM_LIBS, so instruct cmake to also link them.

Index: source/CMakeLists.txt
===================================================================
--- source.orig/CMakeLists.txt
+++ source/CMakeLists.txt
@@ -578,6 +578,7 @@ endif()
 if(SVTHEVC_FOUND)
     target_link_libraries(x265-static ${SVT_HEVC_LIBRARY})
 endif()
+target_link_libraries(x265-static ${PLATFORM_LIBS})
 install(TARGETS x265-static
     LIBRARY DESTINATION ${LIB_INSTALL_DIR}
     ARCHIVE DESTINATION ${LIB_INSTALL_DIR})