Auto merge of #3383 - devnexen:apple_execvP, r=JohnTitor

adding execvP for apple

Author: bors

libc-test/semver/apple.txt

@@ -1883,6 +1883,7 @@ endpwent
 endservent
 endutxent
 exchangedata
+execvP
 faccessat
 fchdir
 fchflags

src/unix/bsd/apple/mod.rs

@@ -6396,6 +6396,11 @@ extern "C" {
         dev: dev_t,
     ) -> ::c_int;
     pub fn freadlink(fd: ::c_int, buf: *mut ::c_char, size: ::size_t) -> ::c_int;
+    pub fn execvP(
+        file: *const ::c_char,
+        search_path: *const ::c_char,
+        argv: *const *mut ::c_char,
+    ) -> ::c_int;
 }
 
 pub unsafe fn mach_task_self() -> ::mach_port_t {