Configure: skip building OpenSSL documentation to conserve time.

The install_sw target first appeared in OpenSSL 0.9.7e and is documented since
OpenSSL 1.0.0 as the way to install the OpenSSL software without documentation.

auto/lib/openssl/make

diff --git a/auto/lib/openssl/make b/auto/lib/openssl/make
index 765cd06..a6090c6 100644
--- a/auto/lib/openssl/make
+++ b/auto/lib/openssl/make
@@ -53,7 +53,7 @@
 	&& if [ -f Makefile ]; then \$(MAKE) clean; fi \\
 	&& ./config --prefix=$ngx_prefix no-shared $OPENSSL_OPT \\
 	&& \$(MAKE) \\
-	&& \$(MAKE) install LIBDIR=lib
+	&& \$(MAKE) install_sw LIBDIR=lib
 
 END