Adds support for auto-detection of compilation databases
from a source file and changes clang-check to make use of this.

This makes clang-check just work on in-tree builds, and allows
easy setup via a symlink per source directory to make clang-check
work without any extra configuration.

llvm-svn: 159990
diff --git a/clang/test/Tooling/auto-detect-from-source-parent.cpp b/clang/test/Tooling/auto-detect-from-source-parent.cpp
new file mode 100644
index 0000000..cb5fd563
--- /dev/null
+++ b/clang/test/Tooling/auto-detect-from-source-parent.cpp
@@ -0,0 +1,8 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/abc/def/ijk/qwe
+// RUN: echo "[{\"directory\":\".\",\"command\":\"clang++ -c %t/abc/def/ijk/qwe/test.cpp\",\"file\":\"%t/abc/def/ijk/qwe/test.cpp\"}]" | sed -e 's/\\/\\\\/g' > %t/compile_commands.json
+// RUN: cp "%s" "%t/abc/def/ijk/qwe/test.cpp"
+// RUN: clang-check "%t/abc/def/ijk/qwe/test.cpp" 2>&1 | FileCheck %s
+
+// CHECK: C++ requires
+invalid;