[X86] Pin debug variable locations mode in pr228950.ll (#231278)
The CHECK lines in pr228950.ll assume instruction-referencing variable
locations, which is the x86_64 default. Under VarLoc-based
LiveDebugValues, llc emits a #DEBUG_VALUE comment between ldtilecfg and
tilezero, and the CHECK-NEXT fails.
Pass -experimental-debug-variable-locations=true so the test does not
depend on the default. This does not change upstream output.
rdar://189810853
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>