Changes to Cross-compiling Tcl between r2 and r3

'''To Windows (x86)'''

$ RC=i586-mingw32msvc-windres AR=i586-mingw32msvc-ar RANLIB=i586-mingw32msvc-ranlib \
   ./configure --host=i586-mingw32msvc --build=i486-slackware-linux --disable-shared \
   --disable-threads --disable-64bit --disable-symbols

----

'''To MIPSEL (uClibc)'''
(blank line)
'''To MIPS (uClibc)'''
(blank line)
$ AR=mipsel-linux-uclibc-ar RANLIB=mipsel-linux-uclibc-ranlib ./configure \
   --host=mipsel-linux-uclibc --build=i486-slackware-linux --disable-shared \
   --disable-threads --disable-64-bit --disable-symbols

Legend

     Only in r2
     Only in r3
     -->      Modified slightly between r2 and r3