cmake: prefer system simpleini library

CMakeModules/FindSimpleIni.cmake

@@ -0,0 +1,19 @@
+# SPDX-FileCopyrightText: 2023 Alexandre Bouvier <contact@amb.tf>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+find_path(SimpleIni_INCLUDE_DIR SimpleIni.h)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(SimpleIni
+    REQUIRED_VARS SimpleIni_INCLUDE_DIR
+)
+
+if (SimpleIni_FOUND AND NOT TARGET SimpleIni::SimpleIni)
+    add_library(SimpleIni::SimpleIni INTERFACE IMPORTED)
+    set_target_properties(SimpleIni::SimpleIni PROPERTIES
+        INTERFACE_INCLUDE_DIRECTORIES "${SimpleIni_INCLUDE_DIR}"
+    )
+endif()
+
+mark_as_advanced(SimpleIni_INCLUDE_DIR)