[CMake] Put headers relative to clang

When libcxx isn't building with an installed LLVM we copy the libcxx headers into the LLVM build directory so that a clang in that build tree can find the headers relative to itself.

This is only important in situations where you don't have headers installed under /, which is common these days on Darwin.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@289963 91177308-0d34-0410-b5e6-96231b3b80d8

include/CMakeLists.txt

@@ -10,18 +10,14 @@ set(LIBCXX_HEADER_PATTERN
   ${LIBCXX_SUPPORT_HEADER_PATTERN}
   )
 
-if (LIBCXX_STANDALONE_BUILD)
-  set(LIBCXX_BUILD_ROOT "${LIBCXX_BINARY_DIR}")
-else()
-  set(LIBCXX_BUILD_ROOT "${LLVM_BINARY_DIR}")
+if(NOT LIBCXX_USING_INSTALLED_LLVM)
+  file(COPY .
+    DESTINATION "${LLVM_BINARY_DIR}/include/c++/v1"
+    FILES_MATCHING
+    ${LIBCXX_HEADER_PATTERN}
+    )
 endif()
 
-file(COPY .
-  DESTINATION "${LIBCXX_BUILD_ROOT}/include/c++/v1"
-  FILES_MATCHING
-  ${LIBCXX_HEADER_PATTERN}
-)
-
 if (LIBCXX_INSTALL_HEADERS)
   install(DIRECTORY .
     DESTINATION include/c++/v1