Fix MinGW make distclean and add <file>.in dependencies.

This patch fixes the crash in MinGW make distclean. The problem
was that vpi/ and driver-vpi/ were being called twice and the
MinGW make was failing on the second call since the Makefile
was already removed.

Add a dependency on config.h and _pli_types.h in the make all
target. It is likely that only _pli_types.h was needed, but
this makes it clear that they need to be rebuilt if the .in
files change.

The lower directories that depend on the top level config.status
now have a target to rebuild the local Makefile file it the
corresponding Makefile.in changes.

driver-vpi/Makefile.in

@@ -58,6 +58,9 @@ clean:
 distclean: clean
 	rm -f Makefile
 
+Makefile: $(srcdir)/Makefile.in ../config.status
+	../config.status --file=$@
+
 O = main.o res.o
 
 iverilog-vpi@EXEEXT@: $O