Add more XFAILs and comments about them.

Author: mstorsjo

libcxx/test/std/input.output/file.streams/fstreams/ifstream.members/offset_range.pass.cpp

@@ -11,8 +11,23 @@
 // Test that we can seek using offsets larger than 32 bit, and that we can
 // retrieve file offsets larger than 32 bit.
 
+// On MSVC targets, we only use the 32 bit fseek/ftell functions. For MinGW
+// targets, we use fseeko/ftello, but the user needs to define
+// _FILE_OFFSET_BITS=64 to make them 64 bit.
+//
 // XFAIL: target={{.*}}-windows{{.*}}
 
+// On 32 bit Android platforms, off_t is 32 bit by default. By defining
+// _FILE_OFFSET_BITS=64, one gets a 64 bit off_t, but the corresponding
+// 64 bit ftello/fseeko functions are only available since Android API 24 (7.0).
+// (On 64 bit Android platforms, off_t has always been 64 bit.)
+//
+// XFAIL: target={{i686|arm.*}}-{{.+}}-android{{.*}}
+
+// Writing the >4 GB test file fails on 32 bit AIX.
+//
+// XFAIL: target=powerpc-{{.+}}-aix{{.*}}
+
 #include <fstream>
 #include <iostream>
 #include <cassert>