[libcxxabi] Document the standalone build's requirements on llvm-config and llvm sources.

The current documentation does not explain that the standalone build requires
the LLVM sources. This patch updates the documentation to reflect this
requirement and explains how to manually specify the location of the required
files.

llvm-svn: 220049

libcxxabi/CMakeLists.txt

@@ -46,7 +46,9 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     set(LLVM_CMAKE_PATH "${LLVM_BINARY_DIR}/share/llvm/cmake")
     set(LLVM_LIT_PATH "${LLVM_PATH}/utils/lit/lit.py")
   else()
-    message(FATAL_ERROR "llvm-config not found and LLVM_MAIN_SRC_DIR not defined")
+    message(FATAL_ERROR "llvm-config not found and LLVM_MAIN_SRC_DIR not defined. "
+                        "Reconfigure with -DLLVM_CONFIG=path/to/llvm-config "
+                        "or -DLLVM_PATH=path/to/llvm-source-root.")
   endif()
 
   if(EXISTS ${LLVM_CMAKE_PATH})

libcxxabi/www/index.html

@@ -96,6 +96,16 @@
     linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++</code></li>
   <li><code>make</code></li>
   </ul>
+  <p> By default CMake uses <code>llvm-config</code> to locate the required
+      LLVM sources. If CMake cannot find <code>llvm-config</code> then you must
+      configure CMake using either of the following options.
+  </p>
+  <ul>
+  <li><code>-DLLVM_CONFIG=path/to/llvm-config</code></li>
+  <li><code>-DLLVM_PATH=path/to/llvm-source-root</code></li>
+  </ul>
+
+  </p>
 
   <p>To run the tests:</p>
   <ul>