Enable >= 2GiB file size support in backupToTar for 32 bit targets.

backupToTar function used in fullbackup currently uses off_t to
represent file sizes which overflows for files having size >= 2 GiB
on 32 bit target architectures.

This CL replaces off_t with off64_t to overcome this limitation.

Fixes: 157633626
Test: atest libandroidfw_tests
Test: Locally running a backup with a test app having a file of size
2GiB and verifying the size variable in backupToTar doesn't overflow
on a 32 bit target.

Change-Id: I404cced810f331ecb9327495ce1f092f1fa2d378
diff --git a/libs/androidfw/Android.bp b/libs/androidfw/Android.bp
index 02c85aa..3893041 100644
--- a/libs/androidfw/Android.bp
+++ b/libs/androidfw/Android.bp
@@ -155,6 +155,7 @@
         android: {
             srcs: [
                 "tests/BackupData_test.cpp",
+		"tests/BackupHelpers_test.cpp",
                 "tests/ObbFile_test.cpp",
                 "tests/PosixUtils_test.cpp",
             ],