[llvm-symbolizer] Unhide and document the '-output-style' option

[ikudrin]

Summary

With the changes from D60770, the option gets useful for users of llvm-symbolizer, not only for the upcoming llvm-addr2line.

[ikudrin]

• Extended an example for the --output-style option.

[jhenderson]

LGTM, with a couple of minor comments.

docs/CommandGuide/llvm-symbolizer.rst

133

preffered -> preferred

135

I think you can remove "the following". Replace "default" with "LLVM".

[ikudrin]

Thanks!

docs/CommandGuide/llvm-symbolizer.rst

 
  Strip directories when printing the file path.
 
 .. option:: -adjust-vma=<offset>
 
  Add the specified offset to object file addresses when performing lookups. This
  can be used to perform lookups as if the object were relocated by the offset.
 
+.. option:: -output-style=<LLVM|GNU>
+
+  Specify the preferred output style. Defaults to ``LLVM``. When the output
+  style is set to ``GNU``, the tool follows the style of GNU's **addr2line**.
+  The differences from the ``LLVM`` style are:
+  
+  * Does not print column of a source code location.
+
+  * Does not add an empty line after the report for an address.
+
+  * Does not replace the name of an inlined function with the name of the
+    topmost caller when inlined frames are not shown and ``-use-symbol-table``
+    is on.
+
+  .. code-block:: console
+
+    $ llvm-symbolizer -p -e=addr.exe 0x40054d 0x400568
+    inc at /tmp/x.c:3:3
+     (inlined by) main at /tmp/x.c:14:0
+
+    main at /tmp/x.c:14:3
+
+    $ llvm-symbolizer --output-style=LLVM -p -i=0 -e=addr.exe 0x40054d 0x400568
+    main at /tmp/x.c:3:3
+
+    main at /tmp/x.c:14:3
+
+    $ llvm-symbolizer --output-style=GNU -p -i=0 -e=addr.exe 0x40054d 0x400568
+    inc at /tmp/x.c:3
+    main at /tmp/x.c:14
+
 EXIT STATUS
 -----------
 
 :program:`llvm-symbolizer` returns 0. Other exit codes imply internal program error.

tools/llvm-symbolizer/llvm-symbolizer.cpp

static cl::list<std::string> ClInputAddresses(cl::Positional,
                                               cl::ZeroOrMore);
 
 static cl::opt<std::string>
     ClFallbackDebugPath("fallback-debug-path", cl::init(""),
                         cl::desc("Fallback path for debug binaries."));
 
 static cl::opt<DIPrinter::OutputStyle>
     ClOutputStyle("output-style", cl::init(DIPrinter::OutputStyle::LLVM),
-                  cl::desc("Specify print style"), cl::Hidden,
+                  cl::desc("Specify print style"),
                   cl::values(clEnumValN(DIPrinter::OutputStyle::LLVM, "LLVM",
                                         "LLVM default style"),
                              clEnumValN(DIPrinter::OutputStyle::GNU, "GNU",
                                         "GNU addr2line style")));
 
 template<typename T>
 static bool error(Expected<T> &ResOrErr) {
   if (ResOrErr)