Some compilers, mostly GCC-derivatives, ignore and warn about trigraphs by default. However, not all compilers ignore these things, as they are a standard "Feature" of the language.
See http://stackoverflow.com/questions/1234582/purpose-of-trigraph-sequences-in-c for more info about the fun of trigraphs.
The following regex can be used to grep for offending files:
Currently the LL source only contains these in the lldiriterator_test.cpp test suite file, so there's no major issues at this point.
EDIT: the above only found trigraphs embedded in strings. However, as Oz noted, trigraphs can cause issues in comments and anywhere else. See below for a better regex - the same as what Oz culled it down to.
More files are affected, and has been done in the linked branch.