The Scalar class gives off the impression that it follows the C type
conversion rules, but this is not true for its host-typed accessor
methods. For example, Scalar((int)-1).ULongLong() returns 0xffffffff,
but (unsigned long long)(int)-1 is 0xffffffffffffffff. I.e., Scalar's
ULongLong always zero-extends, but C semantics require sign-extension.
This patch renames [SU]LongLong to [SZ]ExtOrTruncInt to better reflect
the conversion being done (name chosen after the underlying APInt
operation). Accessors for smaller types are removed completely as the
are not necessary -- normal C conversions from (u)int64_t will handle
that for us in most cases.