build: Fix requiring ell

Make sure libshared-ell is only build if ell is available.
diff --git a/Makefile.am b/Makefile.am
index 322706f..27b6027 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -95,8 +95,7 @@
 				gdbus/mainloop.c gdbus/watch.c \
 				gdbus/object.c gdbus/client.c gdbus/polkit.c
 
-noinst_LTLIBRARIES += src/libshared-glib.la src/libshared-mainloop.la \
-				src/libshared-ell.la
+noinst_LTLIBRARIES += src/libshared-glib.la src/libshared-mainloop.la
 
 shared_sources = src/shared/io.h src/shared/timeout.h \
 			src/shared/queue.h src/shared/queue.c \
@@ -136,8 +135,11 @@
 				src/shared/timeout-mainloop.c \
 				src/shared/mainloop.h src/shared/mainloop.c
 
+if ELL
 src_libshared_ell_la_SOURCES = $(shared_sources) \
 				src/shared/io-ell.c
+noinst_LTLIBRARIES += src/libshared-ell.la
+endif
 
 attrib_sources = attrib/att.h attrib/att-database.h attrib/att.c \
 		attrib/gatt.h attrib/gatt.c \
diff --git a/configure.ac b/configure.ac
index 5132131..2daf1aa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -248,12 +248,13 @@
 		[enable BTP client]), [enable_btpclient=${enableval}])
 AM_CONDITIONAL(BTPCLIENT, test "${enable_btpclient}" = "yes")
 
-if (test "${enable_btpclient}" = "yes"); then
-	PKG_CHECK_MODULES(ELL, ell >= 0.3, dummy=yes,
+if (test "${enable_btpclient}" = "yes" || test "${enable_mesh}" = "yes"); then
+	PKG_CHECK_MODULES(ELL, ell >= 0.3, enable_ell=yes,
 			  AC_MSG_ERROR(ell library >= 0.3 is required))
 	AC_SUBST(ELL_CFLAGS)
 	AC_SUBST(ELL_LIBS)
 fi
+AM_CONDITIONAL(ELL, test "${enable_ell}" = "yes")
 
 AC_ARG_ENABLE(client, AC_HELP_STRING([--disable-client],
 		[disable command line client]), [enable_client=${enableval}])