Add mkfifoat(3).

Looks like I missed one of the *at functions when I added the rest.

Change-Id: If16de82dbf6f9a3ea7bfdcba406ca1c74a3f2279
diff --git a/libc/bionic/mkfifo.cpp b/libc/bionic/mkfifo.cpp
index 08ffad1..a98b350 100644
--- a/libc/bionic/mkfifo.cpp
+++ b/libc/bionic/mkfifo.cpp
@@ -28,6 +28,12 @@
 
 #include <sys/stat.h>
 
+#include <fcntl.h>
+
 int mkfifo(const char* path, mode_t mode) {
-  return mknod(path, (mode & ~S_IFMT) | S_IFIFO, 0);
+  return mkfifoat(AT_FDCWD, path, mode);
+}
+
+int mkfifoat(int fd, const char* path, mode_t mode) {
+  return mknodat(fd, path, (mode & ~S_IFMT) | S_IFIFO, 0);
 }
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index 77d7cac..4900e84 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -181,6 +181,7 @@
 #endif /* defined(__BIONIC_FORTIFY) */
 
 extern int mkfifo(const char*, mode_t);
+extern int mkfifoat(int, const char*, mode_t);
 
 extern int fchmodat(int, const char*, mode_t, int);
 extern int mkdirat(int, const char*, mode_t);