[doxyrest] fix: generator failed to pre-create output directory on posix
[doxyrest] fix: generator failed to pre-create output directory on posix

the reason was: realpath doesn't work for non-existent files (unlike
GetFullPathNameW)

vovkos/doxyrest,vovkos/doxyrest,vovkos/doxyrest,vovkos/doxyrest,vovkos/doxyrest