[libcxx] Add new Sphinx documentation

Summary:
This patch adds Sphinx based documentation to libc++. The goal is to make it easier to write documentation for libc++ since writing new documentation in HTML is cumbersome. This patch rewrites the main page for libc++ along with the instructions for using, building and testing libc++. 

The built documentation can be found and reviewed here: http://efcs.ca/libcxx-docs

In order to build the sphinx documentation you need to specify the cmake options `-DLLVM_ENABLE_SPHINX=ON -DLIBCXX_INCLUDE_DOCS=ON`. This will add the makefile rule `docs-libcxx-html`.

Reviewers: chandlerc, mclow.lists, danalbert, jroelofs

Subscribers: silvas, cfe-commits

Differential Revision: http://reviews.llvm.org/D12129

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245788 91177308-0d34-0410-b5e6-96231b3b80d8

docs/TestingLibcxx.rst

@@ -0,0 +1,142 @@
+==============
+Testing libc++
+==============
+
+.. contents::
+  :local:
+
+Getting Started
+===============
+
+libc++ uses LIT to configure and run its tests. The primary way to run the
+libc++ tests is by using make check-libcxx. However since libc++ can be used
+in any number of possible configurations it is important to customize the way
+LIT builds and runs the tests. This guide provides information on how to use
+LIT directly to test libc++.
+
+Please see the `Lit Command Guide`_ for more information about LIT.
+
+.. _LIT Command Guide: http://llvm.org/docs/CommandGuide/lit.html
+
+
+Setting up the Environment
+--------------------------
+
+After building libc++ you must setup your environment to test libc++ using
+LIT.
+
+#. Create a shortcut to the actual lit executable so that you can invoke it
+   easily from the command line.
+
+   .. code-block:: bash
+
+     $ alias lit='python path/to/llvm/utils/lit/lit.py'
+
+#. Tell LIT where to find your build configuration.
+
+   .. code-block:: bash
+
+     $ export LIBCXX_SITE_CONFIG=path/to/build-libcxx/test/lit.site.cfg
+
+
+LIT Options
+===========
+
+:program:`lit` [*options*...] [*filenames*...]
+
+Command Line Options
+--------------------
+
+To use these options you pass them on the LIT command line as --param NAME or
+--param NAME=VALUE. Some options have default values specified during CMake's
+configuration. Passing the option on the command line will override the default.
+
+.. program:: lit
+
+.. option:: libcxx_site_config=<path/to/lit.site.cfg>
+
+  Specify the site configuration to use when running the tests.  This option
+  overrides the enviroment variable LIBCXX_SITE_CONFIG.
+
+.. option:: libcxx_headers=<path/to/headers>
+
+  Specify the libc++ headers that are tested. By default the headers in the
+  source tree are used.
+
+.. option:: libcxx_library=<path/to/libc++.so>
+
+  Specify the libc++ library that is tested. By default the library in the
+  build directory is used. This option cannot be used when use_system_lib is
+  provided.
+
+.. option:: use_system_lib=<bool>
+
+  **Default**: False
+
+  Enable or disable testing against the installed version of libc++ library.
+  Note: This does not use the installed headers.
+
+.. option:: use_lit_shell=<bool>
+
+  Enable or disable the use of LIT's internal shell in ShTests. If the
+  environment variable LIT_USE_INTERNAL_SHELL is present then that is used as
+  the default value. Otherwise the default value is True on Windows and False
+  on every other platform.
+
+.. option:: no_default_flags=<bool>
+
+  **Default**: False
+
+  Disable all default compile and link flags from being added. When this
+  option is used only flags specified using the compile_flags and link_flags
+  will be used.
+
+.. option:: compile_flags="<list-of-args>"
+
+  Specify additional compile flags as a space delimited string.
+  Note: This options should not be used to change the standard version used.
+
+.. option:: link_flags="<list-of-args>"
+
+  Specify additional link flags as a space delimited string.
+
+.. option:: std=<standard version>
+
+  **Values**: c++98, c++03, c++11, c++14, c++1z
+
+  Change the standard version used when building the tests.
+
+.. option:: debug_level=<level>
+
+  **Values**: 0, 1
+
+  Enable the use of debug mode. Level 0 enables assertions and level 1 enables
+  assertions and debugging of iterator misuse.
+
+.. option:: use_sanitizer=<sanitizer name>
+
+  **Values**: Memory, MemoryWithOrigins, Address, Undefined
+
+  Run the tests using the given sanitizer. If LLVM_USE_SANITIZER was given when
+  building libc++ then that sanitizer will be used by default.
+
+.. option:: color_diagnostics
+
+  Enable the use of colorized compile diagnostics. If the color_diagnostics
+  option is specified or the environment variable LIBCXX_COLOR_DIAGNOSTICS is
+  present then color diagnostics will be enabled.
+
+
+Environment Variables
+---------------------
+
+.. envvar:: LIBCXX_SITE_CONFIG=<path/to/lit.site.cfg>
+
+  Specify the site configuration to use when running the tests.
+  Also see :option:`libcxx_site_config`.
+
+.. envvar:: LIBCXX_COLOR_DIAGNOSTICS
+
+  If ``LIBCXX_COLOR_DIAGNOSTICS`` is defined then the test suite will attempt
+  to use color diagnostic outputs from the compiler.
+  Also see :option:`color_diagnostics`.