Enable rotate left/right tests on all platforms

[tautschnig]

We just need to provide the declarations on non-Clang builds. This is to
ensure test coverage irrespective of whether a test is run using Clang
or not.

• 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

Merging #6605 (0a89ade) into develop (5aae9d0) will increase coverage by 0.01%.
The diff coverage is 90.47%.

@@             Coverage Diff             @@
##           develop    #6605      +/-   ##
===========================================
+ Coverage    76.49%   76.51%   +0.01%     
===========================================
  Files         1578     1578              
  Lines       181464   181464              
===========================================
+ Hits        138816   138844      +28     
+ Misses       42648    42620      -28     

Impacted Files	Coverage Δ
src/solvers/lowering/byte_operators.cpp	92.17% <76.92%> (ø)
src/ansi-c/ansi_c_convert_type.cpp	79.18% <100.00%> (ø)
src/ansi-c/c_storage_spec.cpp	97.56% <100.00%> (ø)
src/ansi-c/parser.y	79.64% <100.00%> (ø)
src/util/c_types.h	100.00% <100.00%> (ø)
src/util/pointer_expr.h	78.77% <100.00%> (ø)
src/util/std_types.cpp	85.86% <100.00%> (ø)
src/util/std_types.h	95.77% <100.00%> (ø)
src/util/type.h	100.00% <100.00%> (ø)
... and 9 more

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