Compiler: move c2_trace functions to libs/c2/c2_trace.c2

[chqrlie]

• add c2_trace.c2 source module in libs/c2 (will later incorporate all
  libs/c2 files in an internal embedded library
• fix stack overflow on recursive inline functions
• generate call tracing tables in c2_trace_tables.c for fast builds

Fix external array definitions:

• accept array definitions without length in interface files
• reject elemsof on arrays of unknown length
• fix external array definitions in C generator
• fix test/interface/incremental_array.c2t: fix external array definition
• fix test/interface/public_by_array_expr.c2t: fix external array definition
• fix test/interface/muti_dimensional_array.c2t: Row and Columns definitions
  were reversed, 2D external array definition in C was incorrect

[bvdberg]

This patch seems to combine 2 things:

• arrays in c2i files
• c2trace refactoring

There is a couple of things i think should change:

• c2trace is now part of libc, with has nothing to do with it
• tracing is now everywhere, in the parser, analyser and generator (it used to be only generator)
• it adds more exceptions (if-statements) for tracing

Overall I think we need some other mechanism to write 'internal' code. Writing this is a c2 file is much better,
than writing it in (raw-)strings. This code should be compiled in IMO, since I dont want the c2c binary to need
internal stuff after compilation. I'll give this some thought..

[chqrlie]

I simplified the port: the source module libs/c2/c2_trace.c2 is added to the target if tracing is enabled and the tables are generated in another module c2_trace_tables for which an interface file is added to the c2 library.

I had to fix the C generator for extern tables as these do not really decay to pointers. (further simplifications pending). I split this into a separate PR to be merged first and separately.

I shall add a way to incorporate the c2 library files in the c2c compiler once the assert and string switch code is moved to c2.

[chqrlie]

I just rebased this PR on the latest master. It should be ready to merge now!