[syslinux] make spotless failure in 3.31

[BuraphaLinux Server]

When I build syslinux, I normally do

make spotless
make

but this fails with syslinux-3.31 because of
4 files:

./com32/lib/sys/vesa/.background.o.d
./com32/lib/sys/vesa/.drawtxt.o.d
./com32/lib/sys/vesa/.alphatbl.o.d
./com32/lib/sys/vesa/.initvesa.o.d

The .initvesa.o.d has some redhat specific path
that does not exist on my system:

  /usr/lib/gcc/x86_64-redhat-linux/4.1.1/include/stdarg.h

If I do this:

make spotless
find . -name '.*.d' -exec rm {} \;
make

then everything is ok.  Please consider adding
the removal of such files to the 'make spotless'
command.