I forgot to update the prototype for LLVMBuildIntCast when correcting

the body to not pass the name for the isSigned parameter.  However it
seems that changing prototypes is a big-no-no, so here I revert the
previous change and pass "true" for isSigned, meaning this always does
a signed cast, which was the previous behaviour assuming the name was
not NULL!  Some other C function needs to be introduced for the general
case of signed or unsigned casts.  This hopefully unbreaks the ocaml
binding.

llvm-svn: 89648