Fix instances of '#if __LP64__'.

Triggers -Wundef, which is on in -Weverything.

Bug: http://b/31496165
Change-Id: Ib06107073f7dd1d584c19c222d0430da9d35630b
diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 58aa6f1..7986ada 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -101,7 +101,7 @@
     sched_param param;
     param.sched_priority = thread->attr.sched_priority;
     if (sched_setscheduler(thread->tid, thread->attr.sched_policy, &param) == -1) {
-#if __LP64__
+#if defined(__LP64__)
       // For backwards compatibility reasons, we only report failures on 64-bit devices.
       error = errno;
 #endif