build: move bitcoin-config.h to its own directory

This allows us to include its path without making other header includes valid.

src/Makefile.am

@@ -17,7 +17,8 @@ $(LIBLEVELDB) $(LIBMEMENV):
           OPT="$(CXXFLAGS) $(CPPFLAGS)"
 endif
 
-BITCOIN_INCLUDES=-I$(builddir) -I$(builddir)/obj $(BOOST_CPPFLAGS) $(LEVELDB_CPPFLAGS)
+BITCOIN_CONFIG_INCLUDES=-I$(builddir)/config
+BITCOIN_INCLUDES=-I$(builddir) -I$(builddir)/obj $(BITCOIN_CONFIG_INCLUDES) $(BOOST_CPPFLAGS) $(LEVELDB_CPPFLAGS)
 
 noinst_LIBRARIES = \
   libbitcoin_server.a \
@@ -219,6 +220,7 @@ EXTRA_DIST = leveldb
 clean-local:
 	-$(MAKE) -C leveldb clean
 	rm -f leveldb/*/*.gcno leveldb/helpers/memenv/*.gcno
+	-rm -f config.h
 
 .rc.o:
 	@test -f $(WINDRES)