Revert "sparc: move exports to definitions"

Revert "sparc: move exports to definitions"

This reverts commit d3867f0483103b8ff7edfdea3ef1981c03d96891 because
symbols exported from assembly don't automatically get modversions (ABI
hashes).

Commit 70a6fcf3283a "[sparc] unify 32bit and 64bit string.h" removed
the export of __memmove; don't try to export it again.  It also
completely disabled declaration of prototypes of memscan, memcpy and
memset, which are defined as macros.  gcc will still generate implicit
calls to memcpy and memset, so restore both exports and prototypes for
them.  Don't restore the export of memscan.

Commit aa95ce361ed9 "sparc64: Delete __ret_efault." did what it says;
don't try to export that symbol.

Commit 1b4af13ff2cc "sparc64: Add __multi3 for gcc 7.x and later."
did what it says; add a prototype and export it from C code instead.

Gbp-Pq: Topic bugfix/sparc
Gbp-Pq: Name revert-sparc-move-exports-to-definitions.patch