title: mingw64 linkder(ld) error: XXX.a: lib file not recognized: File format not recognized
body: <p>I build C++ application with mingw64 in Cygwin.
  If I don't compile the project in a few hours, then I ran into the error that it complains the existing xxx.a lib file not recognized when one CPP file is modified. I have to call make clean and rebuild everything. It's too time-consuming.
  What could cause this trouble?</p>