CMake: support for using LLVM from client projects with find_package.

Patch by arrowdodger!

llvm-svn: 129247
diff --git a/llvm/cmake/modules/LLVMConfigVersion.cmake.in b/llvm/cmake/modules/LLVMConfigVersion.cmake.in
new file mode 100644
index 0000000..add5aa9
--- /dev/null
+++ b/llvm/cmake/modules/LLVMConfigVersion.cmake.in
@@ -0,0 +1 @@
+set(PACKAGE_VERSION "@PACKAGE_VERSION@")
\ No newline at end of file