This adds support for printing the signature sections as part of the
`-p` flag for printing private headers.
The formatting aims to roughly match the formatting used by DXC's
`/dumpbin` flag.
The original version's printed output left some trailing whitespace on
lines, which caused the tests to fail with the strict whitespace
matching.
Re-lands #152531.
Resolves#152380.
be0135538a