While I am sure that gcc libraries (.a) are incompatible with mingw lubraries (also .a), I want to know. Can I cross-compile a windows executable with mingw using the gcc .a library generated for unix systems?
In code form, keep in mind this is a unix system:
cd mylibrarydirectory/
make #produces mylibrary.a
cd ../myprogramdirectory/
gcc -o UnixExecutable mysrc.c -L../mylibrary.a
#and I get a valid unix executable
i586-mingw32msvc-gcc -o Win32Executable.exe mysrc.c -L../mylibrary.a
#will I get a valid windows executable?
No. You have to recompile the library for Windows.
The second command should give an “incompatible library format” or something error. Or at least undefined references to whatever is linked in.