clang: Fix compilation with -openssl-linked

Fixes errors like

qsslsocket_openssl_symbols.cpp:111:6: error:
      unused function 'qsslSocketUnresolvedSymbolWarning'
      [-Werror,-Wunused-function]
void qsslSocketUnresolvedSymbolWarning(const char *functionName)
     ^
1 error generated.

Change-Id: I164518de583f080724ab9a7165c885602a1c6231
Reviewed-by: Richard J. Moore <rich@kde.org>

src/network/ssl/qsslsocket_openssl_symbols.cpp

@@ -107,6 +107,8 @@ QT_BEGIN_NAMESPACE
     possibly with a different version of OpenSSL.
 */
 
+#ifndef QT_LINKED_OPENSSL
+
 namespace {
 void qsslSocketUnresolvedSymbolWarning(const char *functionName)
 {
@@ -119,6 +121,8 @@ void qsslSocketCannotResolveSymbolWarning(const char *functionName)
 }
 }
 
+#endif // QT_LINKED_OPENSSL
+
 #ifdef SSLEAY_MACROS
 DEFINEFUNC3(void *, ASN1_dup, i2d_of_void *a, a, d2i_of_void *b, b, char *c, c, return 0, return)
 #endif