clang-tidy: fix `bugprone-signed-char-misuse` warnings

.clang-tidy

@@ -4,7 +4,6 @@ bugprone-*,\
 -bugprone-macro-parentheses,\
 -bugprone-misplaced-widening-cast,\
 -bugprone-narrowing-conversions,\
--bugprone-signed-char-misuse,\
 -bugprone-suspicious-include,\
 -bugprone-too-small-loop-variable,\
 google-readability-casting,\

Source/cmFileCommand.cxx

@@ -558,8 +558,7 @@ bool HandleStringsCommand(std::vector<std::string> const& args,
       // back subsequent characters
       if ((current_str.length() != num_utf8_bytes)) {
         for (unsigned int j = 0; j < current_str.size() - 1; j++) {
-          c = current_str[current_str.size() - 1 - j];
-          fin.putback(static_cast<char>(c));
+          fin.putback(current_str[current_str.size() - 1 - j]);
         }
         current_str.clear();
       }