cmListFileLexer: Restore 'bracket' member type

Using yy_size_t mismatches the sign in comparisons in our code.
Restore use of 'int'.
Merge topic 'unicode-fstream' into next

bf305c1 cmListFileLexer: Restore 'bracket' member type
Use cmsys::[io]fstream instead of cmsys_ios::[io]fstream.

Also use SystemTools::Fopen() instead of fopen().
This is to eventually support utf-8 filenames.
Merge topic 'unicode-fstream' into next

5730710 Use cmsys::[io]fstream instead of cmsys_ios::[io]fstream.