[clang] [Clang] Fix export declaration diagnostic message (PR #149059)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

> Should I submit another PR to convert the spaces in these two places? @cor3ntin

No, please add a commit to your branch (and push), it will update this PR! Thanks

https://github.com/llvm/llvm-project/pull/149059