systemd: Fix out-of-tree builds

The systemd unit file installation does not work when the build directory
differs from the source directory because cp cannot find the source file.
Prefix the unit files with $(srcdir) to reference files from the source tree.

This fixes out-of-tree builds which use separate build directories (B != S).

Signed-off-by: Khem Raj <raj.khem@gmail.com>

Author: kraj

systemd/Makefile.am

@@ -24,5 +24,5 @@ MAINTAINERCLEANFILES	= Makefile.in
 if INSTALL_SYSTEMD
 install-data-hook: $(unit_files)
 	mkdir -p $(DESTDIR)/$(unitdir)
-	cp $(unit_files) $(DESTDIR)/$(unitdir)
+	cp $(addprefix $(srcdir)/,$(unit_files)) $(DESTDIR)/$(unitdir)
 endif