Actually test linker script processing

[tautschnig]

The goto-cc personality does not invoke linker script processing, hence
the tests located in the ansi-c folder were a no-op. Moving them to the
goto-gcc folder showed that they wouldn't work as is, which is also
fixed now:

1. Add the -N option so as not to generate ELF headers, which those
   linker scripts leave no room for.
2. Make goto-cc accept (but ignore) the -N option. (Cosmetic change
   only.)
3. Actually detect failure of linker script parsing by enabling warnings
   and testing for them.
4. Make sure ls_parse.py is available on the PATH.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[chrisr-diffblue]

Good catch!

[codecov]

Codecov Report

Merging #6578 (4f84963) into develop (4f135cc) will increase coverage by 0.18%.
The diff coverage is 90.86%.

@@             Coverage Diff             @@
##           develop    #6578      +/-   ##
===========================================
+ Coverage    76.01%   76.20%   +0.18%     
===========================================
  Files         1579     1579              
  Lines       181293   181291       -2     
===========================================
+ Hits        137805   138144     +339     
+ Misses       43488    43147     -341     

Impacted Files	Coverage Δ
src/analyses/local_may_alias.cpp	63.80% <0.00%> (ø)
src/cpp/cpp_typecheck_constructor.cpp	89.00% <ø> (ø)
src/cpp/cpp_typecheck_initializer.cpp	29.26% <0.00%> (ø)
src/goto-instrument/contracts/contracts.h	100.00% <ø> (ø)
...trument/contracts/havoc_assigns_clause_targets.cpp	97.72% <ø> (ø)
src/goto-instrument/function.cpp	0.00% <0.00%> (ø)
src/goto-programs/allocate_objects.h	100.00% <ø> (ø)
src/goto-programs/graphml_witness.cpp	53.37% <0.00%> (+0.14%)	⬆️
src/util/c_types.h	100.00% <ø> (ø)
src/goto-programs/string_instrumentation.cpp	25.29% <25.00%> (-0.36%)	⬇️
... and 54 more

---

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