[LAA] Split out a helper to print a collection of memchecks

This is effectively an NFC but we can no longer print the index of the
pointer group so instead I print its address.  This still lets us
cross-check the section that list the checks against the section that
list the groups (see how I modified the test).

E.g. before we printed this:

    Run-time memory checks:
    Check 0:
      Comparing group 0:
        %arrayidxC = getelementptr inbounds i16, i16* %c, i64 %store_ind
        %arrayidxC1 = getelementptr inbounds i16, i16* %c, i64 %store_ind_inc
      Against group 1:
        %arrayidxA = getelementptr i16, i16* %a, i64 %ind
        %arrayidxA1 = getelementptr i16, i16* %a, i64 %add
    ...
    Grouped accesses:
      Group 0:
        (Low: %c High: (78 + %c))
          Member: {%c,+,4}<%for.body>
          Member: {(2 + %c),+,4}<%for.body>

Now we print this (changes are underlined):

    Run-time memory checks:
    Check 0:
      Comparing group (0x7f9c6040c320):
                       ~~~~~~~~~~~~~~
        %arrayidxC1 = getelementptr inbounds i16, i16* %c, i64 %store_ind_inc
        %arrayidxC = getelementptr inbounds i16, i16* %c, i64 %store_ind
      Against group (0x7f9c6040c358):
                     ~~~~~~~~~~~~~~
        %arrayidxA1 = getelementptr i16, i16* %a, i64 %add
        %arrayidxA = getelementptr i16, i16* %a, i64 %ind
    ...
    Grouped accesses:
      Group 0x7f9c6040c320:
            ~~~~~~~~~~~~~~
        (Low: %c High: (78 + %c))
          Member: {(2 + %c),+,4}<%for.body>
          Member: {%c,+,4}<%for.body>

llvm-svn: 243354