A change I'm open to reverting if there is disagreement:

When lldb receives a gdb-remote protocol packet that has
nonprintable characters, it will print the packet in
gdb-remote logging with binary-hex encoding so we don't 
dump random 8-bit characters into the packet log.

I'm changing this check to allow whitespace characters
(newlines, linefeeds, tabs) to be printed if those are
the only non-printable characters in the packet. 

This is primarily to get the response to the 
qXfer:features:read:target.xml packet to show up in the
packet logs in human readable form.  Right now we just
get a dozen kilobytes of hex-ascii and it's hard to 
figure out what register number scheme is being used.

llvm-svn: 247120