Testing of caret location in diagnostic message is currently made with
CHECK directive with the following general format:
CHECK: {{^ \^$}}
James Henderson suggested the following would be more readable:
CHECK: {{^}} ^{{$}}
and when whole lines can be matched (as is the case for command-line
testing where error messages do not include path):
CHECK: ^
using the option --match-full-lines.
This commit implements these 2 changes on all existing caret position
tests. It also aligns the caret to the character it is trying to match
in the above line.