Makefile.am: Make libraries depend on .map files

Without this, an update to the .map file doesn't re-trigger a re-link of
the library.

Change-Id: If0ea6f41730a28b04562d45efa6ca376abaf3f6b
diff --git a/src/gsm/Makefile.am b/src/gsm/Makefile.am
index cff089b..79c5f04 100644
--- a/src/gsm/Makefile.am
+++ b/src/gsm/Makefile.am
@@ -52,6 +52,7 @@
 endif
 
 EXTRA_DIST = libosmogsm.map
+EXTRA_libosmogsm_la_DEPENDENCIES = libosmogsm.map
 
 # Convolutional codes generation
 gsm0503_conv.c: $(top_srcdir)/utils/conv_gen.py $(top_srcdir)/utils/conv_codes_gsm.py