[cfe-dev] Clang tests are using "clang-scan-deps" from host system?

[Xun Li via cfe-dev]

I was playing with modules in Clang.
And I noticed that when running Clang tests, they are using the
"clang-scan-deps" tool from my host system instead of from the build
dir.
For example, if I do:
```
bin/llvm-lit ../clang/test/ClangScanDeps/modules-pch.c -a
```
And look at the output commands, I see things like:
```
: 'RUN: at line 11';   clang-scan-deps -compilation-database
/Users/xun/OSS/llvm-project/build_clang/tools/clang/test/ClangScanDeps/Output/modules-pch.c.tmp/cdb.json
-format experimental-full    -generate-modules-path-args -module
-files-dir /Users/xun/OSS/llvm-project/build_clang/tools/clang/test/ClangScanDeps/Output/modules-pch.c.tmp/build
>> /Users/xun/OSS/llvm-project/build_clang/tools/clang/test/ClangScanDeps/Output/modules-pch.c.tmp/result_pch.json
```
where clang-scan-deps is not using an absolute path. I verified this
by adding "clang-scan-deps --version" in the test, and it matches my
system version, instead of the build version.

Is this a bug?

-- 
Xun