[PATCH] [libcxxabi] Add a cmake build system.

[Logan Chien]

Also, I feel that it will be good to detect for `<stdexcept>` and `<typeinfo>` headers to ensure that libcxx include path has been correctly specified.

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Comment at: CMakeLists.txt:10
@@ +9,3 @@
+
+  # Rely on llvm-config.
+  set(CONFIG_OUTPUT)
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Is there any reason that we have to rely on llvm-config when we are building a standalone version?  I thought libcxxabi does not rely on LLVM (or clang) headers and libraries (except the libcxx headers which should be specified by `-DLIBCXXABI_LIBCXX_INCLUDES`.)

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Comment at: www/index.html:95
@@ +94,3 @@
+  <li><code>mkdir build && cd build</code></li>
+  <li><code>cmake -DLIBCXXABI_LIBCXX_PATH=path/to/libcxx .. # on linux you may need to prefix with CC=clang CXX=clang++</code></li>
+  <li><code>make</code></li>
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One typo here:

    -DLIBCXXABI_LIBCXX_INCLUDES=path/to/libcxx/include

Also, maybe we can suggest to use:

    -DCMAKE_CXX_COMPILER=clang++ 

instead of setting the environment variable here?

http://reviews.llvm.org/D4359