compile on mingw64

[ngama75]

we will try to make it compile and work on windows (at least mingw)

todos

• adjustments to cmake to deal with if (WIN32)
• _win32 assembly files shall be written on the x64 calling convention (or c with intrinsics)
  • cplx/cplx_fft16_avx_fma_win32.s
  • cplx/cplx_ifft16_avx_fma_win32.s
  • @ssmiler reim4/reim4_fftvec_addmul_fma_win32.s -> convert to .c with intrinsics
  • @ssmiler reim4/reim4_fftvec_conv_fma_win32.s -> convert to .c with intrinsics
  • reim/reim_fft16_avx_fma_win32.s keep as .s
  • @ssmiler reim/reim_fft4_avx_fma_win32.s -> convert to .c with intrinsics
  • @ssmiler reim/reim_fft8_avx_fma_win32.s -> convert to .c with intrinsics
  • @ssmiler reim/reim_fftvec_addmul_fma_win32.s -> convert to .c with intrinsics?
  • reim/reim_ifft16_avx_fma_win32.s keep as .s
  • @ssmiler reim/reim_ifft4_avx_fma_win32.s -> convert to .c with intrinsics
  • @ssmiler reim/reim_ifft8_avx_fma_win32.s -> convert to .c with intrinsics
• all 64-bit litterals shall be protected with INT64_C(1) instead of 1L since "L" on windows is 32 bits...
• all printf formats that print 64-bit ints shall use the PRId64 / PRIu64 macros

definition of done:

• it compile with mingw
  • on windows natively
  • cross-compile with x86_64-mingw-w64-gcc-posix
• all unittests shall work
  • on windows natively (msys?)
  • in wine
• readme/wiki documentation on how to compile on windows
• readme/wiki documentation on how to cross-compile + execute