This is only for the frontend, not for stdlib. The implementation is very
slow, optimizing it is the next step.
rdar://16755123 rdar://16013860
Swift SVN r18928
double-quoted string literals that contain a single extended grapheme cluster
SEGCL by default infer type String, but you can ask to infer Character
for them.
Single quoted literals continue to infer Character.
Actual extended grapheme cluster segmentation is not implemented yet,
<rdar://problem/16755123> Implement extended grapheme cluster
segmentation in libSwiftBasic
This is part of
<rdar://problem/16363872> Remove single quoted characters
Swift SVN r17034
