gen_links.sh: auto-generate .gitignore files to ignore symlinks

In each subdir that is a target for symlinks, automatically ignore the results
of gen_links():

- At the top of gen_links.sh.inc, clear the .gitignore.
- In the loop, add each link name to the local .gitignore.
- In selected gen_links.sh, there is also a "manual" link creationg. So that
  this also ends up in the local .gitignore, have the link creation as separate
  gen_link() macro which at the same time adds to ./.gitignore.
- in the root .gitignore, ignore all the subdirs' generated */.gitignore files.

Change-Id: I73c11fe8362358bf7e1bdf0e1be53399b5d3351b
diff --git a/msc/gen_links.sh b/msc/gen_links.sh
index b9cbd0a..fe09155 100755
--- a/msc/gen_links.sh
+++ b/msc/gen_links.sh
@@ -44,7 +44,7 @@
 DIR=../SCCP_CNL113341/src
 FILES="SCCP_Emulation.ttcn  SCCP_EncDec.cc  SCCP_Mapping.ttcnpp  SCCP_Types.ttcn  SCCPasp_Types.ttcn"
 gen_links $DIR $FILES
-ln -s SCCP_Mapping.ttcnpp SCCP_Mapping.ttcn
+gen_link SCCP_Mapping.ttcnpp SCCP_Mapping.ttcn
 
 DIR=$BASEDIR/titan.ProtocolModules.BSSMAP_v11.2.0/src
 FILES="BSSAP_Types.ttcn"