Fix configure -init-submodules ignoring -skip option

When running configure -init-submodules -skip <module>, the -skip
option was ignored because init-repository ran before -skip values
were processed. The skipped modules were still initialized.

Fix by preprocessing -skip values in qt_tl_run_main_script() before
calling qt_ir_run_main_script(). The -skip values are converted to
module-subset exclusions (e.g. -qtwebengine) and merged with the
existing module-subset option.

Also register -skip as a known option in init-repository so it can
be parsed from the optfile.

Fixes: QTBUG-140359
Pick-to: 6.10 6.8
Change-Id: I37ed916dd1c22b6d10d23821044fee807919d4a9
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
(cherry picked from commit 378c8719a9)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

cmake/QtIRCommandLineHelpers.cmake

@@ -178,7 +178,6 @@ function(qt_ir_command_line_set_input name val)
 endfunction()
 
 # Appends a value of a command line option into a global property.
-# Currently unused
 function(qt_ir_command_line_append_input name val)
     if(NOT "${commandline_option_${name}_alias}" STREQUAL "")
         set(name "${commandline_option_${name}_alias}")
@@ -240,6 +239,22 @@ function(qt_ir_commandline_string arg val nextok)
     endif()
 endfunction()
 
+# Like string, but appends to the existing value instead of overwriting.
+# Allows repeated flags like: -skip qtwebengine -skip qtwebview
+function(qt_ir_commandline_addString arg val nextok)
+    if(nextok)
+        qt_ir_args_get_next_command_line_arg(val)
+
+        if("${val}" MATCHES "^-")
+            qt_ir_add_error("No value supplied to command line options '${arg}'.")
+        endif()
+    endif()
+    qt_ir_validate_value("${arg}" "${val}" success)
+    if(success)
+        qt_ir_command_line_append_input("${arg}" "${val}")
+    endif()
+endfunction()
+
 # Sets / handles the value of a command line void option.
 # This is an option like --force, which doesn't take any arguments.
 # Currently unused
@@ -279,6 +294,7 @@ endfunction()
 #
 # Currently handles the following types of CLI arguments:
 #  string
+#  addString (like string, but accumulates values from repeated flags)
 #  boolean
 #  void
 #