[CMake] Allow parent projects to use in-source builds

LLVM checks if it is performing an in-source build and then stop the
build. However, this check is also triggered if LLVM is being build as
part of a parent project, which prevents the parent project itself from
using in-source builds. For example, CMake allows a parent project to
specify the output of its subproject:

add_subdirectory(llvm llvm_build)

This tells CMake to conduct an out-tree build of LLVM, which without
this patch will still fails because what is being tested is the parent
project, not LLVM. This is fixed by using the "CURRENT" variable, which
is only concerned by the CMakeLists that is actually bein processed at
the moment.

Tests:
Ran `make check-llvm`.

Patch by Henrique Jung <henriquenj_AT_gmail_DOT_com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316142 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8d079f0..1435859 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -241,7 +241,7 @@ include(CPack)
 # sure that we don't have any stray generated files lying around in the tree
 # (which would end up getting picked up by header search, instead of the correct
 # versions).
-if( CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE )
+if( CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR AND NOT MSVC_IDE )
   message(FATAL_ERROR "In-source builds are not allowed.
 CMake would overwrite the makefiles distributed with LLVM.
 Please create a directory and run cmake from there, passing the path