Makefile: Avoid changing LIBDIR based on whether it already exists

unix-Makefile.tmpl checks if the target LIBDIR exists on the build
machine or not and based on the result modify the final LIBDIR.
This should be avoided, build results should not depend on the build
machine root filesystem layout. It makes the build results unstable.

The fix simply removes the dir existence test from the unix-Makefile.tmpl.

Fixes: openssl#16121

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16122)

Configurations/unix-Makefile.tmpl

@@ -297,14 +297,7 @@ OPENSSLDIR={- #
               $openssldir -}
 LIBDIR={- our $libdir = $config{libdir};
           unless ($libdir) {
-              #
-              # if $prefix/lib$target{multilib} is not an existing
-              # directory, then assume that it's not searched by linker
-              # automatically, in which case adding $target{multilib} suffix
-              # causes more grief than we're ready to tolerate, so don't...
-              our $multilib =
-                  -d "$prefix/lib$target{multilib}" ? $target{multilib} : "";
-              $libdir = "lib$multilib";
+              $libdir = "lib$target{multilib}";
           }
           file_name_is_absolute($libdir) ? "" : $libdir -}
 # $(libdir) is chosen to be compatible with the GNU coding standards