Fix main() not being visible on Android

A recent change refactored the call to qt_internal_add_executable(),
but that had the unintended side-effect of changing the symbol
visibility from public to hidden. That meant that main() became hidden,
so while apps still built successfully, they could not be run. Restore
the original symbol visibility to fix this regression.

Amends d47278fd09

Pick-to: 6.2
Change-Id: I27d84ab2b0dd013d5c38dcfe55e88f307c4bc5dd
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtExecutableHelpers.cmake

@@ -71,6 +71,14 @@ function(qt_internal_add_executable name)
     endif()
 
     qt_set_common_target_properties(${name})
+    if(ANDROID)
+        # The above call to qt_set_common_target_properties() sets the symbol
+        # visibility to hidden, but for Android, we need main() to not be hidden
+        # because it has to be loadable at runtime using dlopen().
+        set_property(TARGET ${name} PROPERTY C_VISIBILITY_PRESET default)
+        set_property(TARGET ${name} PROPERTY CXX_VISIBILITY_PRESET default)
+    endif()
+
     qt_autogen_tools_initial_setup(${name})
     qt_skip_warnings_are_errors_when_repo_unclean("${name}")