mac-o symbols are prefixed with an underscore. when specifying multiple
sub-regexes (e.g. 'sym1|sym2|sym3'), only the first will be matched
(since the expansion turns into '(?P<symbol>_?sym1|sym2|sym3)'). here,
this is remedied by wrapping the symbol regex in a paren group.
The export symbol regular expression processing is updated to make
several improvements:
* The export expression (export_symbols_regex) now applies to both
functions and global variables
* A named capture group is used to match symbols. This allows the
export expression to contain capture groups without disrupting the
expression matching
