Add goto-ld to .gitignore.

[NlightNFotis]

When building under make, the binary src/goto-cc/goto-ld is not in the
.gitignore file, polluting the git status output.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #5856 (95a0317) into develop (0f9bfa7) will increase coverage by 0.00%.
The diff coverage is 93.69%.

@@           Coverage Diff            @@
##           develop    #5856   +/-   ##
========================================
  Coverage    72.88%   72.88%           
========================================
  Files         1421     1422    +1     
  Lines       154262   154283   +21     
========================================
+ Hits        112434   112455   +21     
  Misses       41828    41828           

Impacted Files	Coverage Δ
src/analyses/goto_check.cpp	88.28% <ø> (ø)
src/util/std_code.h	94.00% <90.90%> (-0.06%)	⬇️
src/util/format_expr.cpp	86.38% <93.02%> (+0.60%)	⬆️
src/goto-instrument/dump_c.cpp	79.97% <100.00%> (-0.08%)	⬇️
src/goto-instrument/goto_program2code.cpp	68.10% <100.00%> (ø)
src/goto-programs/goto_program.h	89.36% <100.00%> (+0.10%)	⬆️
unit/util/format.cpp	100.00% <100.00%> (ø)
src/util/expr_cast.h	94.73% <0.00%> (+0.14%)	⬆️
... and 1 more

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