Add support for building native win32 tools

Add support for compiling the host tools in the tools directory using
the MinGW toolchain.  This produces executables which can be used on
standard Windows computers without requiring cygwin.

One must specify the MinGW compiler and strip utilities as if they
were the host toolchain in order to build win32 executables, eg:

make HOSTCC=i586-mingw32msvc-gcc HOSTSTRIP=i586-mingw32msvc-strip tools

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

tools/ubsha1.c

@@ -21,13 +21,16 @@
  * MA 02111-1307 USA
  */
 
+#include "os_support.h"
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>
 #include <string.h>
+#ifndef __MINGW32__
 #include <sys/mman.h>
+#endif
 #include <sys/stat.h>
 #include "sha1.h"