cmake: prefer system libusb

externals/find-modules/Findlibusb.cmake

@@ -0,0 +1,18 @@
+# SPDX-FileCopyrightText: 2022 Alexandre Bouvier <contact@amb.tf>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+find_package(PkgConfig QUIET)
+if (PKG_CONFIG_FOUND)
+    pkg_search_module(LIBUSB QUIET IMPORTED_TARGET libusb-1.0)
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(libusb
+    REQUIRED_VARS LIBUSB_LINK_LIBRARIES
+    VERSION_VAR LIBUSB_VERSION
+)
+
+if (libusb_FOUND AND NOT TARGET libusb::usb)
+    add_library(libusb::usb ALIAS PkgConfig::LIBUSB)
+endif()