Fixes a regression in 'guix pack -R' introduced with commit
c2dcff41c2. The imported modules of
'c-compiler' would be compiled in this order: first (guix records),
then (guix search-paths). Consequently,
'report-duplicate-field-specifier' would be reported as unbound while
compiling (guix search-paths), leading to a build failure.
* guix/records.scm (report-invalid-field-specifier)
(report-duplicate-field-specifier): Move within 'eval-expand'.