[CMake] Support for monorepo layout

Support finding libcxx and libunwind sources in monorepo style layout.

Differential Revision: https://reviews.llvm.org/D45269

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@329208 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 35eb130..4b1f151 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -99,6 +99,7 @@
   set(LIBCXXABI_LIBCXX_SRC_DIRS
     "${LLVM_MAIN_SRC_DIR}/projects/libcxx"
     "${LLVM_MAIN_SRC_DIR}/runtimes/libcxx"
+    "${LLVM_MAIN_SRC_DIR}/../libcxx"
     )
 endif()
 
@@ -426,6 +427,7 @@
           ${CMAKE_BINARY_DIR}/${LIBCXXABI_LIBUNWIND_INCLUDES}
           ${LLVM_MAIN_SRC_DIR}/projects/libunwind/include
           ${LLVM_MAIN_SRC_DIR}/runtimes/libunwind/include
+          ${LLVM_MAIN_SRC_DIR}/../libunwind/include
     NO_DEFAULT_PATH
     NO_CMAKE_FIND_ROOT_PATH
   )