ubsan: integer overflow in tc-i386.c:offset_in_range

or $9223372036854775808,%eax
runtime error: negation of -9223372036854775808 cannot be represented
in type 'offsetT' (aka 'long'); cast to an unsigned type to negate
this value to itself

	* config/tc-i386.c (offset_in_range): Avoid signed overflow.