build: various fixes

- simplify lua interpreter search
- fix incorrect variable name in BuildLua.cmake
- build PUC Lua with -O2
- silence non-mandatory find_package search for libuv
- simplify Find modules
- Prefer using the explicitly set CI_BUILD over relying on the
  environment variable "CI".

cmake/WindowsDllCopy.cmake

@@ -23,7 +23,7 @@ foreach(DLL_NAME ${DLLS})
     message(FATAL_ERROR "Unable to find dependency ${DLL_NAME}")
   endif()
 
-  if($ENV{CI} MATCHES "true")
+  if(CI_BUILD)
     message("Copying ${DLL_NAME} to ${DST}")
   endif()
   execute_process(COMMAND ${CMAKE_COMMAND} -E copy ${DLL_PATH} ${DST})