Building: make it possible to force linking with static OpenSSL libs

Very simply, support having the .a extension to denote depending on
static libraries.  Note that this is not supported on native Windows
when building shared libraries, as there is not static library then,
just an import library with the same name.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1889)
diff --git a/Configure b/Configure
index 3289e9f..307b1d8 100755
--- a/Configure
+++ b/Configure
@@ -1856,9 +1856,16 @@
                     $d = cleanfile($buildd, $_, $blddir);
                 }
                 # Take note if the file to depend on is being renamed
+                # Take extra care with files ending with .a, they should
+                # be treated without that extension, and the extension
+                # should be added back after treatment.
+                $d =~ /(\.a)?$/;
+                my $e = $1 // "";
+                $d = $`;
                 if ($unified_info{rename}->{$d}) {
                     $d = $unified_info{rename}->{$d};
                 }
+                $d .= $e;
                 $unified_info{depends}->{$ddest}->{$d} = 1;
                 # If we depend on a header file or a perl module, let's make
                 # sure it can get included