v.pref: set DYLD_FALLBACK_LIBRARY_PATH on macos, when -use-coroutines is used, so that v run can work, and the executable can find the downloaded photonwrapper shared library (#23516)

Author: german-swan

vlib/v/pref/pref.v

@@ -987,6 +987,14 @@ pub fn parse_args_and_show_errors(known_external_commands []string, args []strin
 					}
 					res.compile_defines << 'is_coroutine'
 					res.compile_defines_all << 'is_coroutine'
+					$if macos {
+						dyld_fallback_paths := os.getenv('DYLD_FALLBACK_LIBRARY_PATH')
+						so_dir := os.dir(so_path)
+						if !dyld_fallback_paths.contains(so_dir) {
+							env := [dyld_fallback_paths, so_dir].filter(it.len).join(':')
+							os.setenv('DYLD_FALLBACK_LIBRARY_PATH', env, true)
+						}
+					}
 				} $else {
 					println('coroutines only work on macos & linux for now')
 				}