[ELF] - Change i386 i386-pc8.s/i386-pc16.test to work with 8/16 bits values accordingly.

ld.bfd showed error on previous inputs, result values were larger than 8/16 bits,
though ld.gold accepted them.

ABI says "The R_386_16, and R_386_8 relocations truncate the computed 
value to 16-bits and 8-bits respectively".

Patch changes inputs to have result calculated values of relocations to fit 8 and 16 bits.
That can be used for implementation of more strict checks, like bfd do.

Differential revision: https://reviews.llvm.org/D29270

llvm-svn: 293479