compile on mingw64

[ngama75]

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

todos

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

definition of done:

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