Clang warns about this expression in graphite:
if (!m_srAttachTo == 0)
Operator precedence rules require this to be evaluated as:
if ((!m_srAttachTo) == 0)
but clang worries that the author might have intended this to mean:
if (!(m_srAttachTo == 0))
Fortunately these two are equivalent, as is:
if (m_srAttachTo != 0)
and the latter is much easier for humans to understand.

For some reason, --enable-debug adds -Werror to the graphite CFLAGS even
though its makefile.mk specifies:
EXTERNAL_WARNINGS_NOT_ERRORS := TRUE