Revert "libs/libc/stdlib/lib_exit.c: fix multiple definition of __dso_handle in msys2"

This reverts commit 8f96e59.

The implementation of __dso_handle is independent of the HOST OS but dependent on the specific compiler.
Therefore, this patch will cause compilation failures for other cross-compilers on the Windows platform, such as arm-none-eabi-gcc and aarch64-none-elf-gcc.
Constraints should be applied to compiler target rather than compiler host.

Author: zhangshanmin

libs/libc/stdlib/lib_exit.c

@@ -47,10 +47,7 @@
  ****************************************************************************/
 
 extern FAR void *__dso_handle weak_data;
-
-#ifndef CONFIG_HOST_WINDOWS
 FAR void *__dso_handle = &__dso_handle;
-#endif
 
 /****************************************************************************
  * Public Functions