The filter name of a function should match the spelling of the function
name according to the language except that we don't insert _ for unnamed
parameters because underscores are legal inside identifiers and we don't
want to introduce spurious matches (also, we keep the () on a
parameterless function for disambiguation).
rdar://problem/26118915
The internal parameter names are just there to give an extra hint in the
source text for what the argument is. Consequently, we don't want to
allow filtering to match against them.
The code goes into its own sub-tree under 'tools' but tests go under 'test',
so that running 'check-swift' will also run all the SourceKit tests.
SourceKit is disabled on non-darwin platforms.
