Move custom Find modules to their own folder

externals/find-modules/Findgetopt.cmake

@@ -0,0 +1,33 @@
+
+find_package(PkgConfig QUIET)
+pkg_check_modules(PC_getopt QUIET getopt)
+
+find_path(getopt_INCLUDE_DIR
+  NAMES getopt.h
+  PATHS ${PC_getopt_INCLUDE_DIRS}
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(getopt
+  FOUND_VAR getopt_FOUND
+  REQUIRED_VARS
+    getopt_INCLUDE_DIR
+  VERSION_VAR getopt_VERSION
+)
+
+if(getopt_FOUND)
+  set(getopt_INCLUDE_DIRS ${getopt_INCLUDE_DIR})
+  set(getopt_DEFINITIONS ${PC_getopt_CFLAGS_OTHER})
+endif()
+
+if(getopt_FOUND AND NOT TARGET getopt::getopt)
+  add_library(getopt::getopt UNKNOWN IMPORTED)
+  set_target_properties(getopt::getopt PROPERTIES
+    INTERFACE_COMPILE_OPTIONS "${PC_getopt_CFLAGS_OTHER}"
+    INTERFACE_INCLUDE_DIRECTORIES "${getopt_INCLUDE_DIR}"
+  )
+endif()
+
+mark_as_advanced(
+    getopt_INCLUDE_DIR
+)