kernel: add mingw

Add the option to build a cross-compiler for kernel type 'mingw'.
The resulting cross-compiler can be used to build applications on a Linux host
that can be run on a Windows target.

Compiler is build using the mingwrt and w32-api packages aviable from the
MinGW project (http://sourceforge.net/projects/mingw).

The windows headers (w32-api package) are extracting with the kernel_headers
step The libraries and other headers from both packages are build and
installed in the various steps of libc

Signed-off-by: Bart vdr Meulen <bartvdrmeulen@gmail.com>
[yann.morin.1998@anciens.enib.fr: fix kernel headers comment, don't "return 0"]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Configuration file for sstrip tool facility

 # depends on ! BACKEND

 comment "sstrip"

     depends on ARCH_BINFMT_ELF

 config SSTRIP

     bool

     prompt "sstrip"

     depends on ARCH_BINFMT_ELF

     help

       The sstrip utility, to maximise the striping of ELF binaries

       (executables and libraries).

       Buildroot version, forked off the original from ELFkickers.  This one

       is somewhat maintained by the buildroot guys.   

       Supports big-endian systems.