Set fixed locale for numbers near config read/write

[zoltanvb]

Description

Force a fixed locale for numbers. This is a fallback measure when a rogue library modifies the locale, which should be "C" by default.

Related Issues

#15756
In this particular issue, the chain was wayland -> libdecor -> gtk plugin -> setlocale(LC_ALL, "")

There may be some other issues related to this, as the error causes bad reading/writing of floats, leading to all sorts of weird controller setups.

[nfp0]

This has just been fixed on liblocale here: https://gitlab.freedesktop.org/libdecor/libdecor/-/merge_requests/132
Even with that, does RetroArch still benefit from this change?

[zoltanvb]

As discussed under the issue, this change in the current form will avoid the libdecor related problem. Full solution would be locale independent read/write, that is a bigger undertaking, but maybe the issue could remain open as a reminder.

[nfp0]

This might be of interest for this issue:
When using RetroArch on tag v1.16.0.3 and using the fixed libdecor (haven't tested any other combination), I get the following warning:

(retroarch:277159): Gtk-WARNING **: 22:28:54.500: gtk_disable_setlocale() must be called before gtk_init()

[zoltanvb]

I do not see a way how to avoid the warning from RA, unfortunately. Gtk is not used directly from this codebase.

[zoltanvb]

Change is now limited to the problematic configuration.

[LibretroAdmin]

Sorry for the long wait.

[Chandler-Kluser]

Same thing here

retroarch --version
RetroArch - Frontend for libretro
Version: 1.16.0 (Git 3186b1dce3) Nov  5 2023
Compiler: GCC (13.2.1) 64-bit

neofetch
                   -`                    chandler@pc-quarto 
                  .o+`                   ------------------ 
                 `ooo/                   OS: Arch Linux x86_64 
                `+oooo:                  Host: B450 I AORUS PRO WIFI 
               `+oooooo:                 Kernel: 6.6.8-arch1-1 
               -+oooooo+:                Uptime: 7 days, 6 hours, 50 mins 
             `/:-:++oooo+:               Packages: 1852 (pacman) 
            `/++++/+++++++:              Shell: zsh 5.9 
           `/++++++++++++++:             Resolution: 3840x2160 
          `/+++ooooooooooooo/`           DE: GNOME 45.2 
         ./ooosssso++osssssso+`          WM: Mutter 
        .oossssso-````/ossssss+`         WM Theme: Adwaita 
       -osssssso.      :ssssssso.        Theme: HighContrastInverse [GTK2/3] 
      :osssssss/        osssso+++.       Icons: Adwaita [GTK2/3] 
     /ossssssss/        +ssssooo/-       Terminal: kgx 
   `/ossssso+/:-        -:/+osssso+-     CPU: AMD Ryzen 7 3700X (16) @ 3.600GHz 
  `+sso+:-`                 `.-/+oso:    GPU: AMD ATI Radeon RX 6600/6600 XT/6600M 
 `++:.                           `-/+/   Memory: 4744MiB / 15912MiB 
 .`                                 `/