[llvm-dwarfdump] Simplify --ignore-case help text and documentation and fix grammar error

[jhenderson]

Summary

There was a typo in the --ignore-case help text that was copied into the llvm-dwarfdump command-guide. Additionally, this patch simplifies the wording, since it was unnecessarily verbose: the switch applies for searching in general and doesn't need explicitly stating different search modes (which might go out-of-date as options are added or removed).

llvm/trunk/docs/CommandGuide/llvm-dwarfdump.rst

.. option:: -F, --show-form
             Show DWARF form types after the DWARF attribute types.
 
 .. option:: -h, --help
 
             Show help and usage for this command.
 
 .. option:: -i, --ignore-case
 
-            Ignore case distinctions in when searching entries by name
-            or by regular expression.
+            Ignore case distinctions when searching.
 
 .. option:: -n <pattern>, --name=<pattern>
 
             Find and print all debug info entries whose name
             (`DW_AT_name` attribute) matches the exact text in
             <pattern>. Use the :option:`--regex` option to have
             <pattern> become a regular expression for more flexible
             pattern matching.

llvm/trunk/tools/llvm-dwarfdump/llvm-dwarfdump.cpp

 static list<std::string>
     Find("find",
          desc("Search for the exact match for <name> in the accelerator tables "
               "and print the matching debug information entries. When no "
               "accelerator tables are available, the slower but more complete "
               "-name option can be used instead."),
          value_desc("name"), cat(DwarfDumpCategory));
 static alias FindAlias("f", desc("Alias for -find."), aliasopt(Find));
-static opt<bool>
-    IgnoreCase("ignore-case",
-               desc("Ignore case distinctions in when searching by name."),
+static opt<bool> IgnoreCase("ignore-case",
+                            desc("Ignore case distinctions when searching."),
                             value_desc("i"), cat(DwarfDumpCategory));
 static alias IgnoreCaseAlias("i", desc("Alias for -ignore-case."),
                              aliasopt(IgnoreCase));
 static list<std::string> Name(
     "name",
     desc("Find and print all debug info entries whose name (DW_AT_name "
          "attribute) matches the exact text in <pattern>.  When used with the "
          "the -regex option <pattern> is interpreted as a regular expression."),
     value_desc("pattern"), cat(DwarfDumpCategory));