better option wording

Author: vbvictor

clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp

@@ -133,10 +133,9 @@ file, if any.
 static cl::opt<std::string> HeaderFilter("header-filter", desc(R"(
 Regular expression matching the names of the
 headers to output diagnostics from. Diagnostics
-from the main file and all non-system headers 
-of each translation unit are always displayed.
-Set this option to an empty string to disable 
-diagnostics from non-system headers.
+from all non-system headers are displayed by
+default. Diagnostics from the main file of
+each translation unit are always displayed.
 Can be used together with -line-filter.
 This option overrides the 'HeaderFilterRegex'
 option in .clang-tidy file, if any.

clang-tools-extra/docs/clang-tidy/index.rst

@@ -216,10 +216,9 @@ An overview of all the command-line options:
                                        .clang-tidy file, if any.
     --header-filter=<string>         - Regular expression matching the names of the
                                        headers to output diagnostics from. Diagnostics
-                                       from the main file and all non-system headers
-                                       of each translation unit are always displayed.
-                                       Set this option to an empty string to disable 
-                                       diagnostics from non-system headers.
+                                       from all non-system headers are displayed by
+                                       default. Diagnostics from the main file of
+                                       each translation unit are always displayed.
                                        Can be used together with -line-filter.
                                        This option overrides the 'HeaderFilterRegex'
                                        option in .clang-tidy file, if any.