Specify GCC 12 for Cygwin build instructions

[topolarity]

This works around #56840 by installing GCC 12 instead of GCC 13, which fails with the error:

    LINK usr/lib/julia/basecompiler.dll
/usr/lib/gcc/x86_64-w64-mingw32/13/../../../../x86_64-w64-mingw32/bin/ld: /usr/x86_64-w64-mingw32/sys-root/mingw/lib/../lib/dllcrt2.o: in function `_CRT_INIT':
/usr/src/debug/mingw64-x86_64-runtime-13.0.0-1/crt/crtdll.c:82:(.text+0x13b): undefined reference to `_initterm_e'
collect2: error: ld returned 1 exit status

[vtjnash]

SGTM. Though I'm still a bit confused how this error arises, since it successfully links everything up until the system image. Possibly we should use lld to link the system image (just like we'll use it to link the pkgimages)?

[topolarity]

Possibly we should use lld to link the system image (just like we'll use it to link the pkgimages)?

Hmm, seems that with a debug build lld hits similar issues:

lld: error: undefined symbol: __stack_chk_guard━━━━━━━━━━━━━━━━ 0/106
>>> referenced by jl_F83.tmp(text#0.o):(.refptr.__stack_chk_guard)
  ◑ dSFMT_jll -O3
  ◑ dSFMT_jll --check-bounds=yes -O3
...
  ◑ Downloads --check-bounds=yes -O3
lld: error: undefined symbol: __stack_chk_guard
>>> referenced by jl_F2A.tmp(text#0.o):(.refptr.__stack_chk_guard)
lld: error: undefined symbol: __stack_chk_guard
>>> referenced by jl_F17.tmp(text#0.o):(.refptr.__stack_chk_guard)
lld: error: undefined symbol: __stack_chk_guard
>>> referenced by jl_F2D.tmp(text#0.o):(.refptr.__stack_chk_guard)
lld: error: undefined symbol: __stack_chk_guard
>>> referenced by jl_F30.tmp(text#0.o):(.refptr.__stack_chk_guard)
Unhandled Task ERROR: failed process: Process(setenv(`'C:\cygwin64\home\cody\repos\julia\usr\tools\lld.exe' -flavor gnu -m i386pep -Bdynamic --enable-auto-image-base --allow-multiple-definition --disable-auto-import --disable-runtime-pseudo-reloc '' -shared -o 'C:\cygwin64\home\cody\repos\julia\usr\share\julia\compiled\v1.13\Base64\jl_F84.tmp' --whole-archive 'C:\cygwin64\home\cody\repos\julia\usr\share\julia\compiled\v1.13\Base64\jl_F83.tmp' --no-whole-archive '-LC:\cygwin64\home\cody\repos\julia\usr\lib\julia' '-LC:\cygwin64\home\cody\repos\julia\usr\bin' -ljulia-debug -ljulia-internal-debug -lopenlibm -lgcc_s -lgcc -lmsvcrt -lssp`,["ORBIT_UPDATE_INTERVAL=15m0s", "WINDIR=C:\\windows", "TERM=xterm", "ORIGINAL_PATH=/cygdrive/c/windows/system32:/cygdrive/c/windows:/cygdrive/c/windows/System32/Wbem:/cygdrive/c/windows/System32/WindowsPowerShell/v1.0:/cygdrive/c/windows/System32/OpenSSH:%USERPROFILE%/AppData/Local/Microsoft/WindowsApps:/cygdrive/c/Users/cody/AppData/Local/Programs/Espanso", "=::=::\\", "PSMODULEPATH=C:\\Program Files\\WindowsPowerShell\\Modules;C:\\windows\\system32\\WindowsPowerShell\\v1.0\\Modules", "OPENBLAS_MAIN_FREE=1", "PROGRAMFILES=C:\\Program Files", "PROFILEREAD=true", "ALLUSERSPROFILE=C:\\ProgramData"  …  "HOME=C:\\cygwin64\\home\\cody", "PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC", "USERDOMAIN=DELL-TOPOS-MACH", "_=/home/cody/repos/julia/usr/bin/julia-debug.exe", "EXECIGNORE=*.dll", "COMPUTERNAME=DELL-TOPOS-MACH", "APPDATA=C:\\Users\\cody\\AppData\\Roaming", "MAKE_TERMERR=/dev/pty0", "LANG=C", "ONEDRIVE=C:\\Users\\cody\\OneDrive"]), ProcessExited(1)) [1]