We need r334858 for issue 849812.

Trying r335091: https://chromium-review.googlesource.com/c/chromium/src/+/1109394

I think https://reviews.llvm.org/D47578 made installed dir relative in clang-cl, but rolled clang loos not behave like that.

PS C:\src\chromium\src> .\third_party\llvm-build\Release+Asserts\bin\clang-cl.exe -v -no-canonical-prefixes -###
clang version 7.0.0 (trunk 335091)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\src\chromium\src\third_party\llvm-build\Release+Asserts\bin

Why? Chromium clang has something special config when it is built?

Marking this fixed now that the roll is in. Next roll:  https://crbug.com/855772 

tikuta, that's odd. That's not what I'm getting. Before the roll:

C:\src\chromium\src>third_party\llvm-build\Release+Asserts\bin\clang-cl.exe -v -no-canonical-prefixes -###
clang version 7.0.0 (trunk 334100)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\src\chromium\src\third_party\llvm-build\Release+Asserts\bin

After the roll:

C:\src\chromium\src>third_party\llvm-build\Release+Asserts\bin\clang-cl.exe -v -no-canonical-prefixes -###
clang version 7.0.0 (trunk 335091)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: third_party\llvm-build\Release+Asserts\bin

But when I run from PowerShell I get the same result as you:

PS C:\src\chromium\src> third_party\llvm-build\Release+Asserts\bin\clang-cl.exe -v -no-canonical-prefixes -###
clang version 7.0.0 (trunk 335091)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\src\chromium\src\third_party\llvm-build\Release+Asserts\bin

#8, #9
You are right!

PS C:\src\chromium\src> cmd /c third_party\llvm-build\Release+Asserts\bin\clang-cl.exe -v -no-canonical-prefixes -###
clang version 7.0.0 (trunk 335091)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: third_party\llvm-build\Release+Asserts\bin

Seems strange though.
Anyway thank you for finding!

> Why? Chromium clang has something special config when it is built?

Rolled clang is vanilla upstream clang with these cmake args:
https://cs.chromium.org/chromium/src/tools/clang/scripts/update.py?rcl=001e0436c511034494b32f410e01bbd9fd8f6dfa&l=526
https://cs.chromium.org/chromium/src/tools/clang/scripts/update.py?q=update.py&sq=package:chromium&dr=C&l=670

#11 
I see. thanks.

Roll was https://chromium-review.googlesource.com/c/chromium/src/+/1109394 / #569676 (had no Bug: line, so this bug wasn't updated with the commit)