Mac M1 - darwin arm64 supports UCONTEXT passing _xopen_source. We wil…

…l use that as it's more production-ready than pthreads (faster too!) and its passing all tests.

binding.gyp

@@ -55,13 +55,20 @@
 				['OS == "solaris" or OS == "sunos" or OS == "freebsd" or OS == "aix"', {'defines': ['CORO_UCONTEXT']}],
 				['OS == "mac"', {'defines': ['CORO_ASM']}],
 				['OS == "openbsd"', {'defines': ['CORO_ASM']}],
-				['target_arch == "arm" or target_arch == "arm64"',
+				['target_arch == "arm"',
 					{
 						# There's been problems getting real fibers working on arm
 						'defines': ['CORO_PTHREAD'],
 						'defines!': ['CORO_UCONTEXT', 'CORO_SJLJ', 'CORO_ASM'],
 					},
 				],
+				['target_arch == "arm64"',
+					{
+						# There's been problems getting real fibers working on arm
+						'defines': ['CORO_UCONTEXT', '_XOPEN_SOURCE'],
+						'defines!': ['CORO_PTHREAD', 'CORO_SJLJ', 'CORO_ASM'],
+					},
+				],
 			],
 		},
 	],