libc/mingw: do not remove support symlink

Under mingw, it seems that there is a mix between the traditional /usr
directory, and a similar-purposed /mingw directory (both in the sysroot).

Currently, we create /mingw as a symlink to /usr, and we removed it in
the libc-finish step.

Unfortunately, this prevents the pre-processor to find the headers.
Keeping the symlink makes it magically work...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Bare metal config options

config KERNEL_bare_metal

    select BARE_METAL

    help

      'Bare metal' refers to those programs that run without any kernel.

      You probably want to say 'y' here if you plan to use your compiler

      to build bootloaders. It is not yet suitable to build Linux kernels,

      though, because the APCI stuff relies on the target C library headers

      being available?!?!...