Duplicated error messages for static initializers

[alexreg]

The error message could not evaluate static initializer is oddly reported twice for some static initializers (see tests src/test/compile-fail/issue-14227.rs and src/test/compile-fail/issue-28324.rs, for example).

This was discovered in #51110, and the suspected cause is a change @oli-obk recently made to error reporting.

CC @oli-obk @eddyb