Fix instances of '#if __LP64__'.

Triggers -Wundef, which is on in -Weverything.

Bug: http://b/31496165
Change-Id: Ib06107073f7dd1d584c19c222d0430da9d35630b
diff --git a/libc/upstream-openbsd/android/include/gd_qnan.h b/libc/upstream-openbsd/android/include/gd_qnan.h
index e5bf973..bcdff28 100644
--- a/libc/upstream-openbsd/android/include/gd_qnan.h
+++ b/libc/upstream-openbsd/android/include/gd_qnan.h
@@ -23,7 +23,7 @@
 #define d_QNAN0 0x00000000
 #define d_QNAN1 0x7ff80000
 
-#if __LP64__
+#if defined(__LP64__)
 #define ld_QNAN0 0x00000000
 #define ld_QNAN1 0x00000000
 #define ld_QNAN2 0x00000000