Specifier.specified should take offset into account

Prior to this patch, the 'specified' property only considered address and
length.
SIL macros: LEXCMP, LINKOR, LVALUE, and MOVBLK

* Implements LEXCMP, LINKOR, LVALUE, MOVBLK.
* Adds tests for LEXCMP and LVALUE.
* Fixes Specifier.prototype.specified setter.