config: address a number of Coverity issues

Highlights:

• Various memory leaks
• FILE* leaks
• tsize in moveifchanged() is only needed if !changed, and from_sb is only valid if !changed.
• Simplify trivially true expression
• Sanity check elfdump size output (+ fix variable sizes) (des@)

CID: 1471167, 1006391, 1505333, 1505275, 1505349, 1505306, 1505232
Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D38643