Track name changes in the tzdata format

The tzdata format has changed:

Firstly, there is now a "final_offset", which serves as a pointer to the
beginning of the section after the last known section. The pointer means
that file size is no longer a factor when reading the last section and
new sections could be added to the end of the file in future in a
backwards compatible way.

Secondly, since nothing uses zone.tab on Android it is being removed and
the zonetab_offset is replaced by final_offset.

The net effect for bionic is zero besides some comment / name changes.

Test: build only
Change-Id: Ia315083879c891f2d3fc84cf48e304c323ca89f2
diff --git a/libc/tzcode/bionic.cpp b/libc/tzcode/bionic.cpp
index 6d84303..b47f6b0 100644
--- a/libc/tzcode/bionic.cpp
+++ b/libc/tzcode/bionic.cpp
@@ -90,12 +90,12 @@
 // byte[12] tzdata_version  -- "tzdata2012f\0"
 // int index_offset
 // int data_offset
-// int zonetab_offset
+// int final_offset
 struct bionic_tzdata_header_t {
   char tzdata_version[12];
   int32_t index_offset;
   int32_t data_offset;
-  int32_t zonetab_offset;
+  int32_t final_offset;
 };
 static constexpr size_t NAME_LENGTH = 40;
 struct index_entry_t {