Cherry-pick fb3d9153c01b9a560680465190d6ecd804e4c486 into 10.0.1 release

[kadircet]

Bugzilla Link	46278
Resolution	FIXED
Resolved on	Jun 23, 2020 14:29
Version	unspecified
OS	All
Blocks	#44654
CC	@tstellar
Fixed by commit(s)	fb3d915 9706568

Extended Description

Fixes a common clangd crash on c++20 concepts. Fix is a trivial nullptr check and local to clangd.

fix is at fb3d915

[kadircet]

assigned to @sam-mccall

[tstellar]

Fixes a common clangd crash on c++20 concepts. Fix is a trivial nullptr
check and local to clangd.

fix is at
https://github.com/llvm/llvm-project/commit/
fb3d915

Sam, what do you think about backporting this?

[sam-mccall]

LGTM.
Not sure how common -std=c++20 is in the wild, but this is really safe.

[tstellar]

Merged: 9706568