goto-gcc/goto-ld: reproduce original help output

[tautschnig]

There are configure scripts that parse the --help output to obtain the set of supported targets. Without the original output those build systems are then led to believe that we don't support shared libraries (which in turn breaks some builds).

• 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.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@9be731d). Click here to learn what that means.
Patch coverage: 55.55% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #7588   +/-   ##
==========================================
  Coverage           ?   78.50%           
==========================================
  Files              ?     1670           
  Lines              ?   191770           
  Branches           ?        0           
==========================================
  Hits               ?   150552           
  Misses             ?    41218           
  Partials           ?        0           

Impacted Files	Coverage Δ
src/goto-cc/gcc_mode.cpp	68.52% <40.00%> (ø)
src/goto-cc/ld_mode.cpp	36.84% <75.00%> (ø)

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[tautschnig]

See #7590 for the test failure. (Edit: merged, PR rebased.)