build-sys: add version map file to build dependencies

Based on original patch from Jan Engelhardt <jengelh@medozas.de> to
libabc.
diff --git a/Makefile.am b/Makefile.am
index 5247c8d..7661403 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -43,6 +43,7 @@
 libkmod_libkmod_la_LDFLAGS = $(AM_LDFLAGS) \
 	-version-info $(LIBKMOD_CURRENT):$(LIBKMOD_REVISION):$(LIBKMOD_AGE) \
 	-Wl,--version-script=$(top_srcdir)/libkmod/libkmod.sym
+libkmod_libkmod_la_DEPENDENCIES = ${top_srcdir}/libkmod/libkmod.sym
 
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = libkmod/libkmod.pc