We didn't validate that the .word directive was given a sane value,
leading to crashes when we attempt to write out the object file.
Instead, perform some validation and issue a diagnostic pointing at the
start of the diagnostic.
llvm-svn: 251270
For example, ".byte 256" would previously assert() when emitting an object
file. Now it generates a diagnostic that the literal value is out of range.
rdar://9686950
llvm-svn: 134069
