Auto merge of #2767 - carbotaniuman:patch-1, r=Amanieu

Add `stpcpy`, `stpncpy`, and `strtok_r` to unix

These are POSIX 2008 extensions to the C standard.

src/unix/mod.rs

@@ -515,6 +515,8 @@ extern "C" {
 
     pub fn strcpy(dst: *mut c_char, src: *const c_char) -> *mut c_char;
     pub fn strncpy(dst: *mut c_char, src: *const c_char, n: size_t) -> *mut c_char;
+    pub fn stpcpy(dst: *mut c_char, src: *const c_char) -> *mut c_char;
+    pub fn stpncpy(dst: *mut c_char, src: *const c_char, n: size_t) -> *mut c_char;
     pub fn strcat(s: *mut c_char, ct: *const c_char) -> *mut c_char;
     pub fn strncat(s: *mut c_char, ct: *const c_char, n: size_t) -> *mut c_char;
     pub fn strcmp(cs: *const c_char, ct: *const c_char) -> c_int;
@@ -538,6 +540,7 @@ extern "C" {
     )]
     pub fn strerror(n: c_int) -> *mut c_char;
     pub fn strtok(s: *mut c_char, t: *const c_char) -> *mut c_char;
+    pub fn strtok_r(s: *mut c_char, t: *const c_char, p: *mut *mut c_char) -> *mut c_char;
     pub fn strxfrm(s: *mut c_char, ct: *const c_char, n: size_t) -> size_t;
     pub fn strsignal(sig: c_int) -> *mut c_char;
     pub fn wcslen(buf: *const wchar_t) -> size_t;