To support MinGW cross compiler

[mcuee]

This patch is necessary to support MinGW cross compiler.

It is adapted from Arduino avrdude-packing project.
https://github.com/arduino/avrdude-packing/blob/main/patches/0007-Cmake-fix-build-not-working-with-mingw-toolchain.patch

[mcuee]

Without this patch, the failure is like the following github action run.
https://github.com/mcuee/avrdude-packing/actions/runs/3889057820

[ 97%] Linking C executable avrdude
cd /__w/avrdude-packing/avrdude-packing/avrdude/build/src && /usr/bin/cmake -E cmake_link_script CMakeFiles/avrdude.dir/link.txt --verbose=1
/usr/bin/i686-w64-mingw32-gcc -I/opt/lib/i686-w64-mingw32/include/libusb-1.0/ -I/opt/lib/i686-w64-mingw32/include -pthread  -static-libgcc -static-libstdc++ CMakeFiles/avrdude.dir/main.c.o CMakeFiles/avrdude.dir/term.c.o CMakeFiles/avrdude.dir/avrintel.c.o CMakeFiles/avrdude.dir/developer_opts.c.o CMakeFiles/avrdude.dir/whereami.c.o  -o avrdude  libavrdude.a -lm /opt/lib/i686-w64-mingw32/lib/libelf.a /opt/lib/i686-w64-mingw32/lib/libusb.a /opt/lib/i686-w64-mingw32/lib/libusb-1.0.a /opt/lib/i686-w64-mingw32/lib/libhidapi.a /opt/lib/i686-w64-mingw32/lib/libftdi1.a /opt/lib/i686-w64-mingw32/lib/libreadline.a /opt/lib/i686-w64-mingw32/lib/libncurses.a 
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x206): undefined reference to `_imp__WSAStartup@8'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x408): undefined reference to `_imp__gethostbyname@4'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x49f): undefined reference to `_imp__socket@12'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x4b6): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x59b): undefined reference to `_imp__htons@4'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x5d4): undefined reference to `_imp__connect@12'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x5e6): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0xa7e): undefined reference to `_imp__closesocket@4'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0xa88): undefined reference to `_imp__WSACleanup@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0xdaa): undefined reference to `_imp__send@16'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0xdc1): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x134f): undefined reference to `_imp__select@20'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x13c6): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x13d4): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x142d): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x150d): undefined reference to `_imp__recv@16'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1524): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1cb2): undefined reference to `_imp__select@20'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1d24): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1d32): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1d8b): undefined reference to `_imp__WSAGetLastError@0'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1e5d): undefined reference to `_imp__recv@16'
/usr/bin/i686-w64-mingw32-ld: libavrdude.a(ser_win32.c.o):ser_win32.c:(.text+0x1e74): undefined reference to `_imp__WSAGetLastError@0'
collect2: error: ld returned 1 exit status
make[2]: *** [src/CMakeFiles/avrdude.dir/build.make:152: src/avrdude] Error 1
make[2]: Leaving directory '/__w/avrdude-packing/avrdude-packing/avrdude/build'
make[1]: *** [CMakeFiles/Makefile2:98: src/CMakeFiles/avrdude.dir/all] Error 2
make[1]: Leaving directory '/__w/avrdude-packing/avrdude-packing/avrdude/build'
make: *** [Makefile:130: all] Error 2
Error: Process completed with exit code 2.

[mcuee]

#1159 (comment)

If you are targeting Windows, CMake must define WIN32. If not, there is something wrong with your cross-build setup.

I think @mariusgreuel's comment is correct. This is a not a problem of avrdude but rather the cross-compile environment from Arduino avrdude-packing project.

In this case, this PR is invalid.