Unify build documentation and convert to reStructuredText

We now have several options that apply for both libraries and they
shouldn't be documented in multiple files. When already merging
the two Build_With_CMake.txt documents, convert them to
reStructuredText which is used for all of LLVM's documentation.

Differential Revision: https://reviews.llvm.org/D40920

llvm-svn: 321481
diff --git a/openmp/runtime/doc/doxygen/libomp_interface.h b/openmp/runtime/doc/doxygen/libomp_interface.h
index fc92d19..7ff2802 100644
--- a/openmp/runtime/doc/doxygen/libomp_interface.h
+++ b/openmp/runtime/doc/doxygen/libomp_interface.h
@@ -30,8 +30,7 @@
 For the impatient, we cover building the runtime as the first topic here.
 
 CMake is used to build the OpenMP runtime.  For details and a full list of options for the CMake build system,
-see <tt>Build_With_CMake.txt</tt> inside the <tt>runtime/</tt> subdirectory.  These
-instructions will provide the most typical build.
+see <tt>README.rst</tt> in the source code repository.  These instructions will provide the most typical build.
 
 In-LLVM-tree build:.
 @code
@@ -46,7 +45,7 @@
 @code
 $ cd where-you-want-to-live
 Check out openmp
-$ cd where-you-want-to-live/openmp/runtime
+$ cd where-you-want-to-live/openmp
 $ mkdir build && cd build
 $ cmake path/to/openmp -DCMAKE_C_COMPILER=<C compiler> -DCMAKE_CXX_COMPILER=<C++ compiler>
 $ make