Cannot build anymore Fluidsynth with MinGW and CYGWIN.

[carlo-bramini]

Hello, I downloaded the new version 2.4.0 and I tried to update my packages for MinGW and CYGWIN.
Unfortunately, I got some issues which blocked my builds.

(1) It seems that it has been added C90 as minimum dialect when compiling here:

fluidsynth/CMakeLists.txt

Line 122 in 0a86368

set(CMAKE_C_STANDARD 90)

but unfortunately there is this piece of code which blocks the process:

fluidsynth-2.4.0/src/utils/fluid_sys.c:1803:5: error: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
 1803 |     static char ascii_err[sizeof(err)];
      |     ^~~~~~

So, in my opinion the fastest way to fix this issue is to declare err[] and ascii_err[] with the same size, by using a macro.

(2) Fluidsynth now adds _UNICODE and UNICODE on the command line without chance to disable it.
Unfortunately, this is bad because it makes builds of Fluidsynth not working anymore when windows-version is set to 0x0400 and CYGWIN fails with this message:

fluidsynth-2.4.0/src/drivers/fluid_waveout.c:431:20: error: implicit declaration of function ‘wcsicmp’; did you mean ‘wcsncmp’? [-Werror=implicit-function-declaration]
  431 |                 if(wcsicmp(lpwDevName, caps.szPname) == 0)
      |                    ^~~~~~~
      |                    wcsncmp

Actually, CYGWIN provides support for widechar but it is different from the one provided by MinGW and MSVC because wchar_t is 32bit as it is on GLibc for linux, for example. it supports wcscasecmp() instead.
In my opinion, it would be better to make an option like this one into CMakeLists.txt:

option ( enable-unicode "enable UNICODE build for Windows" on )

which is set to on by default, so it will work as it works now if it is not provided.
Later, testing enable-unicode will allow to add or not UNICODE for Windows and CYGWIN.

(3) I got a minor warning when building winmidi driver:

fluidsynth-2.4.0/src/drivers/fluid_winmidi.c:492:15: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long long unsigned int’ [-Wsign-compare]
  492 |         if (n >= sizeof(new_name))
      |               ^~

But hopefully, this is easy to fix since it is just needed to declare n as unsigned int instead of int.

I will provide patches for solving these problems if you want.