VMS: copy prologue/epilogue headers when header files are generated

VMS: copy prologue/epilogue headers when header files are generated

This is crucial when the build tree isn't the source tree, as they
only take effect in directories where included header files reside.

The issue only comes up when linking with the static libraries, since
the shared libraries have upper case aliases of all symbols.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/17755)

(cherry picked from commit 98b7b74122e66f63c4ec67a74e345c64a55c68db)