Do not build a goto-instrument.a

[tautschnig]

The library archive in goto-instrument included several other archives, which
caused spurious failures ("file format not recognized") when trying to link unit
tests.

[kroening]

Is that library even used? As of now it includes goto_instrument_main.cpp, which would make it hard to use it in any executable.
If it is used, there should probably be a LIBRARY_OBJ or the like, which would then not include goto_instrument_main.

[tautschnig]

Is that library even used?

The unit tests use it, maybe that's what should be questioned and changed. Happy to go down that route instead.

[tautschnig]

I have reworked this to completely remove the goto-instrument.a unicorn.

[peterschrammel]

Fine with this.
Just to mention that the cmake build handles that correctly by building a goto-instrument lib without goto_instrument_main and then builds the executable linking with the lib.

[tautschnig]

Just to mention that the cmake build handles that correctly by building a goto-instrument lib without goto_instrument_main and then builds the executable linking with the lib.

Yes - and doing so in the Makefile builds would possibly be cleaner, but then we should do it in all folders (as CMake does).