build: create missing directories for out-of-tree builds

They could be created by dumb luck with dependency tracking, but
apparently some distributions disable that.

Makefile.am

@@ -288,6 +288,7 @@ DBUS_INTERFACE_DOCS = \
 	docs/api/dbus-org.freedesktop.NetworkManager.DnsManager.xml
 
 introspection/%.c: introspection/%.xml
+	@$(MKDIR_P) introspection
 	$(AM_V_GEN) gdbus-codegen \
 		--generate-c-code $(basename $@) \
 		--generate-docbook docs/api/dbus \
@@ -558,10 +559,12 @@ EXTRA_DIST += \
 	libnm-core/crypto_gnutls.c \
 	libnm-core/crypto_nss.c
 
-libnm-core/nm-vpn-dbus-types.xml: libnm-core/nm-vpn-dbus-interface.h tools/enums-to-docbook.pl
+libnm-core/nm-vpn-dbus-types.xml: libnm-core libnm-core/nm-vpn-dbus-interface.h tools/enums-to-docbook.pl
+	@$(MKDIR_P) libnm-core
 	$(AM_V_GEN) @PERL@ $(srcdir)/tools/enums-to-docbook.pl 'nm-vpn-dbus-types' 'VPN Plugin D-Bus API Types' $^ >$@
 
-libnm-core/nm-dbus-types.xml: libnm-core/nm-dbus-interface.h tools/enums-to-docbook.pl
+libnm-core/nm-dbus-types.xml: libnm-core libnm-core/nm-dbus-interface.h tools/enums-to-docbook.pl
+	@$(MKDIR_P) libnm-core
 	$(AM_V_GEN) @PERL@ $(srcdir)/tools/enums-to-docbook.pl 'nm-dbus-types' 'NetworkManager D-Bus API Types' $^ >$@
 
 BUILT_SOURCES += \
@@ -3340,7 +3343,7 @@ udevrules_DATA = \
 endif
 
 data/server.conf: $(srcdir)/data/server.conf.in
-	@mkdir -p data/
+	@$(MKDIR_P) data/
 	$(AM_V_GEN) $(data_edit) $< >$@
 
 EXTRA_DIST += \
@@ -3951,7 +3954,7 @@ endif
 ###############################################################################
 
 man/common.ent: man/common.ent.in
-	@mkdir -p man/
+	@$(MKDIR_P) man/
 	$(AM_V_GEN) $(data_edit) $< >$@
 
 xsltproc_flags = \

configure.ac

@@ -33,6 +33,7 @@ AM_PROG_CC_C_O
 AC_PROG_CXX
 
 AC_PROG_LN_S
+AC_PROG_MKDIR_P
 
 # Prefer gcc-* variants; the ones libtool would choose don't work with LTO
 AC_CHECK_TOOLS(AR, [gcc-ar ar], false)