Improve formatting of for loops and multi-variable DeclStmts.

This combines several related changes:
a) Don't break before after the variable types in for loops with a
   single variable.
b) Better indent DeclStmts defining multiple variables.

Before:
bool aaaaaaaaaaaaaaaaaaaaaaaaa =
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(aaaaaaaaaaaaaaaa),
     bbbbbbbbbbbbbbbbbbbbbbbbb =
         bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb(bbbbbbbbbbbbbbbb);
for (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
         aaaaaaaaaaa = aaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaa;
     aaaaaaaaaaa != aaaaaaaaaaaaaaaaaaa; ++aaaaaaaaaaa) {
}

After:
bool aaaaaaaaaaaaaaaaaaaaaaaaa =
         aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(aaaaaaaaaaaaaaaa),
     bbbbbbbbbbbbbbbbbbbbbbbbb =
         bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb(bbbbbbbbbbbbbbbb);
for (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaaaaa =
         aaaaaaaaaaaaaaaa.aaaaaaaaaaaaaaa;
     aaaaaaaaaaa != aaaaaaaaaaaaaaaaaaa; ++aaaaaaaaaaa) {
}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178641 91177308-0d34-0410-b5e6-96231b3b80d8