Add private API for finding symbols on Linux

Add an API for use by declarative that allows searching for a
symbol that has been loaded, without opening a specific library.
This makes it possible for declarative to determine if the
profiling library has been preloaded, and to call functions on
it that enable / disable / save the current profile.

Change-Id: I2ec12d9babea2a152990c19735e98d4d7c10a062
Reviewed-by: Martin Jones <martin.jones@nokia.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

src/corelib/plugin/qlibrary_unix.cpp

@@ -258,6 +258,13 @@ bool QLibraryPrivate::unload_sys()
     return true;
 }
 
+#ifdef Q_OS_LINUX
+Q_CORE_EXPORT QFunctionPointer qt_linux_find_symbol_sys(const char *symbol)
+{
+    return QFunctionPointer(dlsym(RTLD_DEFAULT, symbol));
+}
+#endif
+
 #ifdef Q_OS_MAC
 Q_CORE_EXPORT QFunctionPointer qt_mac_resolve_sys(void *handle, const char *symbol)
 {