[sanitizers] Restore internal_readlink for x32

r316591 has

@@ -389,13 +383,11 @@ uptr internal_dup2(int oldfd, int newfd) {
 }

 uptr internal_readlink(const char *path, char *buf, uptr bufsize) {
-#if SANITIZER_NETBSD
-  return internal_syscall_ptr(SYSCALL(readlink), path, buf, bufsize);
-#elif SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
+#if SANITIZER_USES_CANONICAL_LINUX_SYSCALLS
   return internal_syscall(SYSCALL(readlinkat), AT_FDCWD,
                           (uptr)path, (uptr)buf, bufsize);
 #else
-  return internal_syscall(SYSCALL(readlink), (uptr)path, (uptr)buf, bufsize);
+  return internal_syscall_ptr(SYSCALL(readlink), path, buf, bufsize);
 #endif
 }

which dropped the (uptr) cast and broke x32.  This patch puts back the
(uptr) cast to restore x32 and fixes:

https://bugs.llvm.org/show_bug.cgi?id=40783

Differential Revision: https://reviews.llvm.org/D58413

llvm-svn: 354451