Documentation: add information about builtin includes to FAQ

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174612 91177308-0d34-0410-b5e6-96231b3b80d8

docs/FAQ.rst

@@ -51,3 +51,14 @@ driver and add the option you need.  Alternatively, you can run
 ``clang -Xclang <option> ...`` to force the driver pass ``<option>`` to
 ``clang -cc1``.
 
+I get errors about some headers being missing (``stddef.h``, ``stdard.h``)
+--------------------------------------------------------------------------
+
+Some header files (``stddef.h``, ``stdard.h``, and others) are shipped with
+Clang --- these are called builtin includes.  Clang searches for them in a
+directory relative to the location of the ``clang`` binary.  If you moved the
+``clang`` binary, you need to move the builtin headers, too.
+
+More information can be found in the :ref:`libtooling_builtin_includes`
+section.
+

docs/LibTooling.rst

@@ -168,6 +168,9 @@ arguments:
   $ export BD=/path/to/build/llvm
   $ $BD/bin/clang-check -p $BD tools/clang/tools/clang-check/ClangCheck.cpp
 
+
+.. _libtooling_builtin_includes:
+
 Builtin includes
 ^^^^^^^^^^^^^^^^