Set TZDEFAULT to NULL.

TZDEFAULT not applicable to bionic as there is no file per time
zone mapping.

Bug: 25413083

Test: CtsLibcoreTestCases
Test: CtsLibcoreOjTestCases
Test: CtsBionicTestCases
Change-Id: Ie489b5b2cda6c6f623f32e5413da77ec5eaa823f
diff --git a/libc/Android.bp b/libc/Android.bp
index c8df591..3ee7c0a 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -262,6 +262,8 @@
         "-DTHREAD_SAFE=1",
         // The name of the tm_gmtoff field in our struct tm.
         "-DTM_GMTOFF=tm_gmtoff",
+        // TZDEFAULT is not applicable to Android as there is no one file per time zone mapping
+        "-DTZDEFAULT=NULL",
         // Where we store our tzdata.
         "-DTZDIR=\"/system/usr/share/zoneinfo\"",
         // Include `tzname`, `timezone`, and `daylight` globals.