This patch is related to the one I posted yesterday to make 
with_target_charset do something reasonable in the absence of ICONV support:

https://sourceware.org/ml/gdb-patches/2015-09/msg00357.html

If GDB is configured without ICONV support, the target wide charset 
defaults to "ISO-8859-1" (which isn't even a wide charset), and all the 
wide strings in this test print as gibberish.  Otherwise, GDB seems to 
think the default is "auto; currently UTF-32", so let's make the 
dependency on UTF-32 explicit here and bail out if it's not available.

OK to commit?

-Sandra