cmake: move find-modules to root cmake dir

CMakeModules/FindDiscordRPC.cmake

@@ -0,0 +1,27 @@
+# SPDX-FileCopyrightText: 2022 Alexandre Bouvier <contact@amb.tf>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+find_path(DiscordRPC_INCLUDE_DIR discord_rpc.h)
+
+find_library(DiscordRPC_LIBRARY discord-rpc)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(DiscordRPC
+    REQUIRED_VARS
+        DiscordRPC_LIBRARY
+        DiscordRPC_INCLUDE_DIR
+)
+
+if (DiscordRPC_FOUND AND NOT TARGET DiscordRPC::discord-rpc)
+    add_library(DiscordRPC::discord-rpc UNKNOWN IMPORTED)
+    set_target_properties(DiscordRPC::discord-rpc PROPERTIES
+        IMPORTED_LOCATION "${DiscordRPC_LIBRARY}"
+        INTERFACE_INCLUDE_DIRECTORIES "${DiscordRPC_INCLUDE_DIR}"
+    )
+endif()
+
+mark_as_advanced(
+    DiscordRPC_INCLUDE_DIR
+    DiscordRPC_LIBRARY
+)