Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -119,6 +119,7 @@
 set(LIBCXXABI_GCC_TOOLCHAIN "" CACHE STRING "GCC toolchain for cross compiling.")
 set(LIBCXXABI_SYSROOT "" CACHE STRING "Sysroot for cross compiling.")
 set(LIBCXXABI_LIBCXX_LIBRARY_PATH "" CACHE STRING "The path to libc++ library.")
+set(LIBCXX_ABI_MAJOR_VERSION 1 CACHE STRING "Major ABI version of libc++.")
 
 # Default to building a shared library so that the default options still test
 # the libc++abi that is being built. There are two problems with testing a
@@ -133,15 +134,21 @@
   message(FATAL_ERROR "libc++abi must be built as either a shared or static library.")
 endif()
 
-find_path(
-  LIBCXXABI_LIBCXX_INCLUDES
-  vector
-  PATHS ${LIBCXXABI_LIBCXX_INCLUDES}
-        ${LIBCXXABI_LIBCXX_PATH}/include
-        ${CMAKE_BINARY_DIR}/${LIBCXXABI_LIBCXX_INCLUDES}
-        ${LLVM_MAIN_SRC_DIR}/projects/libcxx/include
-        ${LLVM_INCLUDE_DIR}/c++/v1
-  )
+if (NOT "${LLVM_MAIN_SRC_DIR}" STREQUAL "")
+  # When building as part of LLVM, libc++ headers will end up under
+  # ${CMAKE_BINARY_DIR}. They are not there yet, so we can not use find_path.
+  set(LIBCXXABI_LIBCXX_INCLUDES
+    ${CMAKE_BINARY_DIR}/include/c++/v${LIBCXX_ABI_MAJOR_VERSION})
+else()
+  find_path(
+    LIBCXXABI_LIBCXX_INCLUDES
+    vector
+    PATHS ${LIBCXXABI_LIBCXX_INCLUDES}
+          ${CMAKE_BINARY_DIR}/include/c++/v${LIBCXX_ABI_MAJOR_VERSION}
+          ${CMAKE_BINARY_DIR}/${LIBCXXABI_LIBCXX_INCLUDES}
+          ${LLVM_INCLUDE_DIR}/c++/v${LIBCXX_ABI_MAJOR_VERSION}
+    )
+endif()
 
 set(LIBCXXABI_LIBCXX_INCLUDES "${LIBCXXABI_LIBCXX_INCLUDES}" CACHE PATH
     "Specify path to libc++ includes." FORCE)