[libc++][doc] Fixes FeatureTestMacroTable.html.

[Mordante]

Summary

utils/generate_feature_test_macro_components.py uses the wrong
indentation. :name: feature-status-table :widths: auto is rendered as
text instead of being used by Sphinx to render the table properly.

This fixes the identation in the souce and updates the generated output.

[ldionne]

Thanks for fixing!

libcxx/docs/FeatureTestMacroTable.rst

 This file documents the feature test macros currently supported by libc++.
 
 .. _feature-status:
 
 Status
 ======
 
 .. table:: Current Status
-     :name: feature-status-table
-     :widths: auto
 
     ================================================= =================
     Macro Name                                        Value
     ================================================= =================
     **C++ 14**
     -------------------------------------------------------------------
     ``__cpp_lib_chrono_udls``                         ``201304L``
     ------------------------------------------------- -----------------

libcxx/utils/generate_feature_test_macro_components.py

 This file documents the feature test macros currently supported by libc++.
 
 .. _feature-status:
 
 Status
 ======
 
 .. table:: Current Status
-     :name: feature-status-table
-     :widths: auto
 
 {status_tables}
 
 """.format(status_tables=create_table(get_status_table(), 4))
 
   table_doc_path = os.path.join(docs_path, 'FeatureTestMacroTable.rst')
   with open(table_doc_path, 'w', newline='\n') as f:
     f.write(doc_str)