Changes

buildsystem: move related scripts to subdir

Clean up the main directory by moving all buildsystem related scripts
into a _buildsystem subdirectory.

Rename gen_links.sh.inc to gen_links.inc.sh while at it, so vim does
syntax highlighting as shell script and not bitbake.

The rest of these patches in this series lead up to changing the
buildsystem to build out-of-tree (so we don't clutter the source dirs
with symlinks and build artifacts) and making the build output more
readable.

Related: OS#6599
Change-Id: Ieeefdfd74b2698794fb12fec4ed32565dc9f36a6

buildsystem/regen_makefile: change to inc script

Make the regen_makefile script more consistent with gen_links.inc.sh by
also turning it into an include script. By doing this all previously
declared variables are available in regen_makefile, which means export
and passing as arguments is not needed anymore, making the resulting
users simpler.

Use #!/bin/sh -e while at it and remove empty CPPFLAGS_TTCN3 vars.

Change-Id: I10a41671e857024be6a5e8577c2aaca83228793e

buildsystem: remove ttcn3_compiler workaround

The related debian bug has been fixed in 2018, so remove the workaround.
I've also verified that the binary is called "compiler" in Arch Linux
(as some developers are on Arch).

Change-Id: Ia50aa3caffeaa85eefba10695096aa23dcb69c93