introduce widen_if_needed

[kroening]

This introduces a macro widen_if_needed(s) to replace the common pattern

 #ifdef _MSC_VER
  std::ifstream infile(widen(file));
 #else
  std::ifstream infile(file);
 #endif

by the shorter and less redundant

std::ifstream infile(widen_if_needed(file));

• 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.
• 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

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (f33b96a) 78.62% compared to head (f06ff71) 78.62%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7938      +/-   ##
===========================================
- Coverage    78.62%   78.62%   -0.01%     
===========================================
  Files         1701     1701              
  Lines       195975   195974       -1     
===========================================
- Hits        154087   154086       -1     
  Misses       41888    41888              

Files	Coverage Δ
src/ansi-c/c_preprocess.cpp	35.06% <100.00%> (ø)
src/cbmc/cbmc_parse_options.cpp	78.62% <100.00%> (ø)
src/goto-analyzer/show_on_source.cpp	94.82% <100.00%> (ø)
src/goto-cc/compile.cpp	73.55% <100.00%> (ø)
src/goto-cc/gcc_message_handler.cpp	86.66% <100.00%> (ø)
src/goto-checker/solver_factory.cpp	79.66% <100.00%> (ø)
src/goto-instrument/unwindset.cpp	86.60% <100.00%> (ø)
src/goto-programs/read_goto_binary.cpp	55.66% <100.00%> (ø)
src/cprover/cprover_parse_options.cpp	56.25% <0.00%> (ø)
src/goto-cc/cl_message_handler.cpp	0.00% <0.00%> (ø)
... and 3 more

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.