build: syms: fix *.def file for mach-o binary format

There was a missing trailing newline which caused some warnings when calling
`ld`.
build: syms: reindent

We avoided reindenting this in the past to allow merging upstream changes.
In hindsight these are very unlikely and we are actually doing changes on
the code, so it's better to have the correct indentation and formatting in
our source file.