x86_64-w64-mingw32 test FAIL t-scanf.c:1477: GNU MP assertion failed: ret == (-1)

[paul zimmermann]

       Torbjörn,

> Should we pass this option for mingw on GMP's configure.ac?
> Or do people expect broken libc on this platform...?

note we have this in MPFR INSTALL file:

3 - To avoid using the Microsoft runtime (which might not be conform to ISO C),
    you can use the MinGW runtime package (which is an integral part of MinGW).
    For example, with MinGW versions 3.15 and later you can get an
    ISO-compliant printf() if you compile your application with either
    '-ansi', '-posix' or '-D__USE_MINGW_ANSI_STDIO'. In order to have the
    MPFR formatted output functions based on ISO-compliant printf(), you
    need to compile GMP (not MPFR) with CC="gcc -D__USE_MINGW_ANSI_STDIO"
    (since the standard printf modifiers %e, %Ld and %td are passed to GMP).
    Not doing so may result in failures of some of the printf-related tests.
    For instance, the following error on some Windows machine has been
    reported:

      https://sympa.inria.fr/sympa/arc/mpfr/2016-02/msg00053.html

      Error in mpfr_vsprintf (s, "%e", ...);
      expected: "-1.250000e+000"
      got:      "-1.250000e+00"
      FAIL tsprintf.exe (exit status: 1)

    The cause is that here the C functions vsnprintf and vsprintf used
    internally in GMP do not produce the same output:

      https://sympa.inria.fr/sympa/arc/mpfr/2016-03/msg00045.html
      https://sympa.inria.fr/sympa/arc/mpfr/2016-03/msg00051.html
      https://sympa.inria.fr/sympa/arc/mpfr/2016-03/msg00053.html

    Building MPFR with -D__USE_MINGW_ANSI_STDIO is currently useless except
    for some error messages in the test suite.

Paul