Windows: avoid using 'rem' in the nmake makefile

Windows: avoid using 'rem' in the nmake makefile

To avoid the possibility that someone creates rem.exe, rem.bat or
rem.cmd, simply don't use it.  In the cases it was used, it was to
avoid empty lines, but it turns out that nmake handles those fine, so
no harm done.

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/6686)

(cherry picked from commit 1b6a0a261e22eb5a574bdb75da208817ffa2fbba)