Fix the Makefiles.

Optimized (BMI2+PGO) builds for Linux+Windows.

See Makefile.bmi2 and use:
    make -f Makefile.bmi2 gull.syzygy.linux
    make -f Makefile.bmi2 gull.syzygy.windows

For Windows cross compilation is not supported.  Instead use MSYS2 configured
for 64-bit compilation.

Linux results (self-play versus old non-syzygy non-BMI2 Gull.linux):

LTC (60"+0.6", 1-thread, 6-man syzygy):

    Score: +1728-1351=6921
    Number of games: 10000
    Winning fraction: 0.51885
    Elo difference: +13.1045
    LOS: 1

STC (10"+0.1", 1-thread, 6-man syzygy):

    Score: +2040-1791=6169
    Number of games: 10000
    Winning fraction: 0.51245
    Elo difference: +8.65293
    LOS: 0.999971

Windows build has not yet been tested.

Optimized (BMI2+PGO) builds for Linux+Windows.

See Makefile.bmi2 and use:
    make -f Makefile.bmi2 gull.syzygy.linux
    make -f Makefile.bmi2 gull.syzygy.windows

For Windows cross compilation is not supported.  Instead use MSYS2 configured
for 64-bit compilation.

Linux results (self-play versus old non-syzygy non-BMI2 Gull.linux):

LTC (60"+0.6", 1-thread, 6-man syzygy):

    Score: +1728-1351=6921
    Number of games: 10000
    Winning fraction: 0.51885
    Elo difference: +13.1045
    LOS: 1

STC (10"+0.1", 1-thread, 6-man syzygy):

    Score: +2040-1791=6169
    Number of games: 10000
    Winning fraction: 0.51245
    Elo difference: +8.65293
    LOS: 0.999971

Windows build has not yet been tested.

Add a "tablebase hits" (tbhits) counter.

This version is thread safe.

Add a "tablebase hits" (tbhits) counter.

This version is thread safe.

Port Gull Linux back to Windows.

Requires cross-compilation using MinGW.  Not yet tested.

Fix README.

Fix #2

Issue #2 appears to be a copy-and-paste bug in gen_captures.

Fix #1