x86emul/test: don't use *_len symbols

x86emul/test: don't use *_len symbols

... as they don't work as intended with -fPIC.

I did prefer them over *_end ones at the time because older gcc would
cause .L* symbols to be public, due to issuing .globl for all
referenced externals. And labels at the end of instructions collide
with the ones at the start of the next instruction, making disassembly
harder to grok. Luckily recent gcc no longer issues those .globl
directives, and hence .L* labels, staying local by default, no longer
get in the way.

Reported-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Tested-by: Wei Liu <wei.liu2@citrix.com>