Add C linkage for __open_2 and __openat_2.

Otherwise Clang mangle them with C++ names.

Change-Id: I844e28d834df8b0752b32d2aadd2013fc8804a43
diff --git a/libc/bionic/open.cpp b/libc/bionic/open.cpp
index e0dd181..52c34dc 100644
--- a/libc/bionic/open.cpp
+++ b/libc/bionic/open.cpp
@@ -50,7 +50,7 @@
   return __openat(AT_FDCWD, pathname, flags, mode);
 }
 
-int __open_2(const char* pathname, int flags) {
+extern "C" int __open_2(const char* pathname, int flags) {
   if (__predict_false(flags & O_CREAT)) {
     __fortify_chk_fail("open(O_CREAT): called without specifying a mode", 0);
   }
@@ -75,7 +75,7 @@
   return __openat(fd, pathname, flags, mode);
 }
 
-int __openat_2(int fd, const char* pathname, int flags) {
+extern "C" int __openat_2(int fd, const char* pathname, int flags) {
   if (flags & O_CREAT) {
     __fortify_chk_fail("openat(O_CREAT): called without specifying a mode", 0);
   }