[clang] [clang] more useful error message for decomposition declaration missing initializer (PR #127924)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Please provide more details than a link to the github issue. The summary is what goes in the git log and folks downstream often use git log as a first line in analyzing issues. Summaries w/o detailed summary are not useful.

https://github.com/llvm/llvm-project/pull/127924