Add support for darwin to core:c/libc

core/c/libc/errno.odin

@@ -4,6 +4,8 @@ package libc
 
 when ODIN_OS == "windows" {
 	foreign import libc "system:libucrt.lib"
+} else when ODIN_OS == "darwin" {
+	foreign import libc "system:System.framework"
 } else {
 	foreign import libc "system:c"
 }
@@ -38,6 +40,20 @@ when ODIN_OS == "windows" {
 	ERANGE :: 34
 }
 
+when ODIN_OS == "darwin" {
+	@(private="file")
+	@(default_calling_convention="c")
+	foreign libc {
+		@(link_name="__error")
+		_get_errno :: proc() -> ^int ---
+	}
+
+	// Unknown
+	EDOM   :: 33
+	EILSEQ :: 92
+	ERANGE :: 34
+}
+
 // Odin has no way to make an identifier "errno" behave as a function call to
 // read the value, or to produce an lvalue such that you can assign a different
 // error value to errno. To work around this, just expose it as a function like