Add dependency tracking to sdksyms.c and export composite wrapper.

Thanks to David Miller for noticing a make problem with sdksyms.c
not being regenerated when sdksyms.sh is updated. This is not yet the
best solution; automake generates dependency for sdksyms.o, but the
build really should also regenerate sdksyms.c when sdksyms.o needs to
be regenerated.
  Export the symbols in miext/cw/cw.h. These symbols are in libxaa, and
at least the nvidia driver uses them. Maybe cw.h should be installed
in the sdk.

hw/xfree86/loader/Makefile.am

@@ -23,5 +23,5 @@ libloader_la_SOURCES = \
 
 CLEANFILES = sdksyms.c
 
-sdksyms.c:
+sdksyms.c: sdksyms.sh
 	$(srcdir)/sdksyms.sh $(AM_CFLAGS) $(CFLAGS) $(INCLUDES)