Fix detection of wxWidgets toolkit

wxWidgets_CONFIG_OPTIONS can be utilised to explicitly select GTK2 or GTK3. It
must be evaluated when querying the toolkit to avoid a mismatch between the
version actually used and the version KiCad assumes to be used.

Reapplied the original version. The previous patch has been modified
under an invalid assumption of being incompatible with msys2.

CMakeLists.txt

@@ -565,7 +565,8 @@ include( ${wxWidgets_USE_FILE} )
 
 # Check the toolkit used to build wxWidgets
 execute_process(
-    COMMAND sh -c "${wxWidgets_CONFIG_EXECUTABLE} ${wxWidgets_CONFIG_OPTIONS} --query-toolkit"
+    COMMAND sh "${wxWidgets_CONFIG_EXECUTABLE}"
+        ${wxWidgets_CONFIG_OPTIONS} --query-toolkit
     RESULT_VARIABLE wxWidgets_TOOLKIT_RESULT
     OUTPUT_VARIABLE wxWidgets_TOOLKIT_FOUND
     OUTPUT_STRIP_TRAILING_WHITESPACE