build: tweak PKG_CHECK_MODULES calls

There's no need to call AC_SUBST after a PKG_CHECK_MODULES call, since
the variables are always set. As an example: the produced Makefile.in
and Makefile are identical before/after this change.

Similarly, we don't need the "dummy=yes" and manual AC_MSG_ERROR() call
- pkg-config (or pkgconf) will produce the same and in some cases better
  error messages.

configure.ac

@@ -72,23 +72,16 @@ AC_CHECK_LIB(dl, dlopen, dummy=yes,
 
 AC_CHECK_HEADERS(linux/types.h linux/if_alg.h linux/uinput.h linux/uhid.h sys/random.h)
 
-PKG_CHECK_MODULES(GLIB, glib-2.0 >= 2.28, dummy=yes,
-				AC_MSG_ERROR(GLib >= 2.28 is required))
-AC_SUBST(GLIB_CFLAGS)
-AC_SUBST(GLIB_LIBS)
+PKG_CHECK_MODULES(GLIB, glib-2.0 >= 2.28)
 
 if (test "${enable_threads}" = "yes"); then
 	AC_DEFINE(NEED_THREADS, 1, [Define if threading support is required])
-	PKG_CHECK_MODULES(GTHREAD, gthread-2.0 >= 2.16, dummy=yes,
-				AC_MSG_ERROR(GThread >= 2.16 is required))
+	PKG_CHECK_MODULES(GTHREAD, gthread-2.0 >= 2.16)
 	GLIB_CFLAGS="$GLIB_CFLAGS $GTHREAD_CFLAGS"
 	GLIB_LIBS="$GLIB_LIBS $GTHREAD_LIBS"
 fi
 
-PKG_CHECK_MODULES(DBUS, dbus-1 >= 1.10, dummy=yes,
-				AC_MSG_ERROR(D-Bus >= 1.10 is required))
-AC_SUBST(DBUS_CFLAGS)
-AC_SUBST(DBUS_LIBS)
+PKG_CHECK_MODULES(DBUS, dbus-1 >= 1.10)
 
 AC_ARG_WITH([dbusconfdir], AS_HELP_STRING([--with-dbusconfdir=DIR],
 				[path to D-Bus configuration directory]),
@@ -230,10 +223,7 @@ AM_CONDITIONAL(MONITOR, test "${enable_monitor}" != "no")
 AC_ARG_ENABLE(udev, AS_HELP_STRING([--disable-udev],
 		[disable udev device support]), [enable_udev=${enableval}])
 if (test "${enable_tools}" != "no" && test "${enable_udev}" != "no"); then
-	PKG_CHECK_MODULES(UDEV, libudev >= 172, dummy=yes,
-				AC_MSG_ERROR(libudev >= 172 is required))
-	AC_SUBST(UDEV_CFLAGS)
-	AC_SUBST(UDEV_LIBS)
+	PKG_CHECK_MODULES(UDEV, libudev >= 172)
 	AC_CHECK_LIB(udev, udev_hwdb_new,
 		AC_DEFINE(HAVE_UDEV_HWDB_NEW, 1,
 			[Define to 1 if you have the udev_hwdb_new() function.]))
@@ -260,30 +250,21 @@ AC_ARG_ENABLE(mesh, AS_HELP_STRING([--enable-mesh],
 AM_CONDITIONAL(MESH, test "${enable_mesh}" = "yes")
 
 if (test "${enable_mesh}" = "yes"); then
-	PKG_CHECK_MODULES(JSONC, json-c >= 0.13, dummy=yes,
-				AC_MSG_ERROR(json-c >= 0.13 is required))
-	AC_SUBST(JSON_CFLAGS)
-	AC_SUBST(JSON_LIBS)
+	PKG_CHECK_MODULES(JSONC, json-c >= 0.13)
 fi
 
 AC_ARG_ENABLE(midi, AS_HELP_STRING([--enable-midi],
                 [enable MIDI support]), [enable_midi=${enableval}])
 AM_CONDITIONAL(MIDI, test "${enable_midi}" = "yes")
 
 if (test "${enable_midi}" = "yes"); then
-	PKG_CHECK_MODULES(ALSA, alsa, dummy=yes,
-			AC_MSG_ERROR(ALSA lib is required for MIDI support))
-	AC_SUBST(ALSA_CFLAGS)
-	AC_SUBST(ALSA_LIBS)
+	PKG_CHECK_MODULES(ALSA, alsa)
 fi
 
 AC_ARG_ENABLE(obex, AS_HELP_STRING([--disable-obex],
 		[disable OBEX profile support]), [enable_obex=${enableval}])
 if (test "${enable_obex}" != "no"); then
-	PKG_CHECK_MODULES(ICAL, libical, dummy=yes,
-					AC_MSG_ERROR(libical is required))
-	AC_SUBST(ICAL_CFLAGS)
-	AC_SUBST(ICAL_LIBS)
+	PKG_CHECK_MODULES(ICAL, libical)
 fi
 AM_CONDITIONAL(OBEX, test "${enable_obex}" != "no")
 
@@ -295,10 +276,7 @@ AC_ARG_ENABLE([external_ell], AS_HELP_STRING([--enable-external-ell],
 				[enable external Embedded Linux library]),
 					[enable_external_ell=${enableval}])
 if (test "${enable_external_ell}" = "yes"); then
-	PKG_CHECK_MODULES(ELL, ell >= 0.39, dummy=yes,
-		AC_MSG_ERROR(Embedded Linux library >= 0.39 is required))
-	AC_SUBST(ELL_CFLAGS)
-	AC_SUBST(ELL_LIBS)
+	PKG_CHECK_MODULES(ELL, ell >= 0.39)
 fi
 if (test "${enable_external_ell}" != "yes" &&
 		(test "${enable_btpclient}" = "yes" || test "${enable_mesh}" = "yes")); then
@@ -442,17 +420,11 @@ AC_ARG_ENABLE(android, AS_HELP_STRING([--enable-android],
 AM_CONDITIONAL(ANDROID, test "${enable_android}" = "yes")
 
 if (test "${enable_android}" = "yes"); then
-	PKG_CHECK_MODULES(SBC, sbc >= 1.2, dummy=yes,
-			AC_MSG_ERROR(SBC library >= 1.2 is required))
-	AC_SUBST(SBC_CFLAGS)
-	AC_SUBST(SBC_LIBS)
+	PKG_CHECK_MODULES(SBC, sbc >= 1.2)
 fi
 
 if (test "${enable_android}" = "yes"); then
-	PKG_CHECK_MODULES(SPEEXDSP, speexdsp >= 1.2, dummy=yes,
-			AC_MSG_ERROR(SPEEXDSP library >= 1.2 is required))
-	AC_SUBST(SPEEXDSP_CFLAGS)
-	AC_SUBST(SPEEXDSP_LIBS)
+	PKG_CHECK_MODULES(SPEEXDSP, speexdsp >= 1.2)
 fi
 
 AC_DEFINE_UNQUOTED(ANDROID_STORAGEDIR, "${storagedir}/android",
@@ -466,15 +438,8 @@ if (test -z "${plugin_phonebook}"); then
 fi
 
 if (test "${plugin_phonebook}" = "ebook"); then
-	PKG_CHECK_MODULES(LIBEBOOK, [libebook-1.2 >= 3.3], dummy=yes,
-			AC_MSG_ERROR(libebook >= 3.3 is required))
-	AC_SUBST(LIBEBOOK_CFLAGS)
-	AC_SUBST(LIBEBOOK_LIBS)
-	PKG_CHECK_MODULES(LIBEDATESERVER, [libedataserver-1.2 >= 3.3],
-			dummy=yes,
-			AC_MSG_ERROR(libedataserver >= 3.3 is required))
-	AC_SUBST(LIBEDATESERVER_CFLAGS)
-	AC_SUBST(LIBEDATESERVER_LIBS)
+	PKG_CHECK_MODULES(LIBEBOOK, libebook-1.2 >= 3.3)
+	PKG_CHECK_MODULES(LIBEDATESERVER, libedataserver-1.2 >= 3.3)
 fi
 AC_SUBST(PLUGIN_PHONEBOOK, [${plugin_phonebook}])