sys/posix: impl rest of linux, impl some of Windows

core/sys/posix/string_libc.odin

@@ -0,0 +1,30 @@
+#+build linux, windows, darwin, netbsd, openbsd, freebsd
+package posix
+
+when ODIN_OS == .Windows {
+	foreign import lib "system:libucrt.lib"
+} else when ODIN_OS == .Darwin {
+	foreign import lib "system:System.framework"
+} else {
+	foreign import lib "system:c"
+}
+
+// string.h - string operations
+
+// NOTE: most of the symbols in this header are not useful in Odin and have been left out.
+
+foreign lib {
+	/*
+	Map the error number to a locale-dependent error message string.
+
+	Returns: a string that may be invalidated by subsequent calls
+
+	[[ More; https://pubs.opengroup.org/onlinepubs/9699919799/functions/strerror.html ]]
+	*/
+	@(link_name="strerror")
+	_strerror :: proc(errnum: Errno) -> cstring ---
+}
+
+strerror :: #force_inline proc "contextless" (errnum: Maybe(Errno) = nil) -> cstring {
+	return _strerror(errnum.? or_else errno())
+}