Update hints on how to link to OpenSSL

The traditional way to fix building against a custom OpenSSL is to set the
OPENSSL_LIBS environment variable.

Anyhow, since Qt 5.6 there's a more generic way to configure
linking against external libraries by configuring the <LIB>_INCDIR, <LIB>_LIBDIR,
<LIB>_PREFIX, <LIB>_LIBS, <LIB>_LIBS_DEBUG and <LIB>_LIBS_RELEASE
qmake variables at configure time. Using these have following advantages:

- Can handle different libs for a -debug-and-release build
- Can be used also for other libs than just openssl

So let's try to promote this.

Also update any examples for OpenSSL 1.1.

Change-Id: I24dbccdd87d0fc50bf31c6afe7aa692d4b810fb7
Reviewed-by: Jörg Bornemann <[email protected]>

src/network/configure.json

@@ -352,9 +352,10 @@
             "condition": "features.openssl-linked && libs.openssl.source != 0
                           && input.openssl.prefix == '' && input.openssl.libs == '' && input.openssl.libs.debug == ''",
             "message": "When linking against OpenSSL, you can override the default
-library names through OPENSSL_LIBS.
+library names and directories with setting OPENSSL_PREFIX (or OPENSSL_INCDIR, OPENSSL_LIBDIR),
+and OPENSSL_LIBS, OPENSSL_LIBS_DEBUG, OPENSSL_LIBS_RELEASE.
 For example:
-    OPENSSL_LIBS='-L/opt/ssl/lib -lssl -lcrypto' ./configure -openssl-linked"
+    ./configure -openssl-linked OPENSSL_PREFIX='/opt/ssl' OPENSSL_LIBS='-lssl -lcrypto'"
         },
         {
             "type": "warning",

src/network/doc/src/ssl.qdoc

@@ -55,12 +55,11 @@
     When building a version of Qt linked against OpenSSL, the build system will
     attempt to link with libssl and libcrypt libraries located in the default
     location on the developer's system. This location is configurable:
-    set the \c OPENSSL_LIBS environment variable to contain the linker options
-    required to link Qt against the installed library. For example, on a Unix/Linux
+    set the \c OPENSSL_LIBDIR command line argument. For example, on Unix/Linux
     system:
 
     \code
-        OPENSSL_LIBS='-L/opt/ssl/lib -lssl -lcrypto' ./configure -openssl-linked
+        ./configure -openssl-linked OPENSSL_LIBDIR=/usr/local/ssl
     \endcode
 
     To disable SSL support in a Qt build, configure Qt with the \c{-no-openssl}

src/network/ssl/ssl.pri

@@ -102,9 +102,9 @@ qtConfig(ssl) {
         # Add optional SSL libs
         # Static linking of OpenSSL with msvc:
         #   - Binaries http://slproweb.com/products/Win32OpenSSL.html
-        #   - also needs -lUser32 -lAdvapi32 -lGdi32 -lCrypt32
+        #   - also needs -lWs2_32 -lGdi32 -lAdvapi32 -lCrypt32 -lUser32
         #   - libs in <OPENSSL_DIR>\lib\VC\static
-        #   - configure: -openssl -openssl-linked -I <OPENSSL_DIR>\include -L <OPENSSL_DIR>\lib\VC\static OPENSSL_LIBS="-lUser32 -lAdvapi32 -lGdi32" OPENSSL_LIBS_DEBUG="-lssleay32MDd -llibeay32MDd" OPENSSL_LIBS_RELEASE="-lssleay32MD -llibeay32MD"
+        #   - configure: -openssl-linked -openssl-linked OPENSSL_INCDIR="%OPENSSL_DIR%\include" OPENSSL_LIBDIR="%OPENSSL_DIR%\lib\VC\static" OPENSSL_LIBS="-lWs2_32 -lGdi32 -lAdvapi32 -lCrypt32 -lUser32" OPENSSL_LIBS_DEBUG="-llibssl64MDd -llibcrypto64MDd" OPENSSL_LIBS_RELEASE="-llibssl64MD -llibcrypto64MD"
 
         qtConfig(openssl-linked): \
             QMAKE_USE_FOR_PRIVATE += openssl