Don't undefine __STRICT_ANSI__ for mingw

[tobil4sk]

This was done originally for #785. However, since gcc 11.1.0, this gives a warning:

In file included from /usr/x86_64-w64-mingw32/include/c++/13.1.0/bits/exception.h:36,
                 from /usr/x86_64-w64-mingw32/include/c++/13.1.0/typeinfo:34,
                 from /.../hxcpp/include/hxcpp.h:27,
                 from /.../hxcpp/src/hx/Lib.cpp:1:
/usr/x86_64-w64-mingw32/include/c++/13.1.0/x86_64-w64-mingw32/bits/c++config.h:666:2: warning: #warning "__STRICT_ANSI__ seems to have been undefined; this is not supported" [-Wcpp]
  666 | #warning "__STRICT_ANSI__ seems to have been undefined; this is not supported"
      |  ^~~~~~~

This is due to this change: https://gcc.gnu.org/git/?p=gcc.git;a=commit;f=libstdc%2B%2B-v3/include/bits/c%2B%2Bconfig;h=767537a8b027bcb5807bb45b0268c5da98c2c7a0

The original problem in #785 doesn't happen with mingw-w64. The original mingw project is outdated (and 32 bit only) so it is safe remove this flag now. Compilation with the original mingw is already broken anyway:

Mingw compilation errors

``` Error: D:/hxcpp/src/hx/Thread.cpp:628:2: error: 'CONDITION_VARIABLE' does not name a type CONDITION_VARIABLE cond; ^ D:/hxcpp/src/hx/Thread.cpp: In constructor 'hxCondition::hxCondition()': D:/hxcpp/src/hx/Thread.cpp:641:31: error: 'cond' was not declared in this scope InitializeConditionVariable(&cond); ^ D:/hxcpp/src/hx/Thread.cpp:641:35: error: 'InitializeConditionVariable' was not declared in this scope InitializeConditionVariable(&cond); ^ D:/hxcpp/src/hx/Thread.cpp: In member function 'void hxCondition::Wait()': D:/hxcpp/src/hx/Thread.cpp:711:30: error: 'cond' was not declared in this scope SleepConditionVariableCS(&cond,&cs,INFINITE); ^ D:/hxcpp/src/hx/Thread.cpp:711:47: error: 'SleepConditionVariableCS' was not declared in this scope SleepConditionVariableCS(&cond,&cs,INFINITE); ^ D:/hxcpp/src/hx/Thread.cpp: In member function 'bool hxCondition::TimedWait(double)': D:/hxcpp/src/hx/Thread.cpp:721:43: error: 'cond' was not declared in this scope return (bool)SleepConditionVariableCS(&cond, &cs, (DWORD)((FLOAT)timeout * 1000.0)); ^ D:/hxcpp/src/hx/Thread.cpp:721:86: error: 'SleepConditionVariableCS' was not declared in this scope return (bool)SleepConditionVariableCS(&cond, &cs, (DWORD)((FLOAT)timeout * 1000.0)); ^ D:/hxcpp/src/hx/Thread.cpp: In member function 'void hxCondition::Signal()': D:/hxcpp/src/hx/Thread.cpp:744:27: error: 'cond' was not declared in this scope WakeConditionVariable(&cond); ^ D:/hxcpp/src/hx/Thread.cpp:744:31: error: 'WakeConditionVariable' was not declared in this scope WakeConditionVariable(&cond); ^ D:/hxcpp/src/hx/Thread.cpp: In member function 'void hxCondition::Broadcast()': D:/hxcpp/src/hx/Thread.cpp:753:30: error: 'cond' was not declared in this scope WakeAllConditionVariable(&cond); ^ D:/hxcpp/src/hx/Thread.cpp:753:34: error: 'WakeAllConditionVariable' was not declared in this scope WakeAllConditionVariable(&cond); ```

[Simn]

This PR has a conflict now.

[tobil4sk]

Finally green, thanks! @Simn