[NFC][LLVM] Make test resilent to value of use-constant-*-splat flags.

Ensure Transforms/Reassociate/fast-ReassociateVector.ll passes when
UseConstantIntForFixedLengthSplat defaults to true.

Author: paulwalker-arm

llvm/test/Transforms/Reassociate/fast-ReassociateVector.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -passes=reassociate -S | FileCheck %s --check-prefixes=CHECK,CHECK-CV
+; RUN: opt < %s -passes=reassociate -S -use-constant-int-for-fixed-length-splat=false | FileCheck %s --check-prefixes=CHECK,CHECK-CV
 ; RUN: opt < %s -passes=reassociate -S -use-constant-int-for-fixed-length-splat | FileCheck %s --check-prefixes=CHECK,CHECK-CI
 
 ; Check that a*c+b*c is turned into (a+b)*c