regcomp.c: Refactor macro so works on EBCDIC, clarity

regcomp.c: Refactor macro so works on EBCDIC, clarity

_C_C_T was being passed both a test and the value to put the test on, whereas
the value is actually setup inside the macro, which is not a clean interface,
and would not work on EBCDIC, as the loop bounds are for ASCII.  By just
passing the test name, the macro can generate code that will work also on
EBCDIC.

Unfortunately, the same can't happen for the NOLOC version of the macro, as it
needs to look at more than a single byte, so needs an address.