collect2.exe: error: ld returned 5 exit status

Just in case someone finds this due the same problem, please, add the following flag to your compiler -Wl,--verbose (or --verbose to the linker). This will show which library was not found or give you more information about the problem.

I had the same issue. I link my project with static library. After mingw64 upgrade, my project stoped building with the same error. I found out that debug version built successfully. So i compared linker flags. In release version Qt add this flags "-Wl,-s,--relax,--gc-section". I couldn't find any information about "-s" flag, but due to this link i figured out that -gc-section flag was the reason of fail. I added the following code to my .pro-file, and it worked

mingw {
        contains(QT_ARCH, x86_64): {
            LIBS+=-Wl,--no-gc-sections
        }
}