[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

2 files changed, 13 insertions, 1 deletions

diff --git a/libcxxabi/CMakeLists.txt b/libcxxabi/CMakeLists.txt
index 6815b0d9828..494b18d7b79 100644
--- a/libcxxabi/CMakeLists.txt
+++ b/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})
diff --git a/libcxxabi/www/index.html b/libcxxabi/www/index.html
index 197e71755e1..b7b66d8c552 100644
--- a/libcxxabi/www/index.html
+++ b/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>