file: Restore error capture in undocumented READ_ELF mode

Brad Kingrequested to merge
brad.king/cmake:file-READ_ELF-capture-error into master

Revise the error message added by !6240 (merged) to honor the CAPTURE_ERROR option. This is needed by the call site in BundleUtilities to suppress errors on non-ELF files.

Fixes: #23074 (closed)
Backport: release

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