[Hexagon, test] Fix use of undef FileCheck var

[thopre]

Summary

LLVM test CodeGen/Hexagon/hwloop3.ll tries to check for the absence of a
sequence of consecutive instructions with several CHECK-NOT with one of
those directives using a variable defined in another. However CHECK-NOT
are checked independently so that is using a variable defined in a
pattern that should not occur in the input.

This commit merges the two CHECK-NOT into a single CHECK-NOT that
matches the content of two successive non-blank lines, thereby allowing
to preserve the intent of the test.

llvm/test/CodeGen/Hexagon/hwloop3.ll

 ; RUN: llc -march=hexagon < %s | FileCheck %s
 ;
 ; Remove the unconditional jump to following instruction.
 
 ; CHECK: endloop0
-; CHECK-NOT: jump [[L1:.]]
-; CHECK-NOT: [[L1]]
+; CHECK-NOT: jump [[L1:.]]{{.*[[:space:]]+}}[[L1]]
 
 define void @test(i32* nocapture %a, i32 %n) nounwind {
 entry:
   br label %for.body
 
 for.body:
   %arrayidx.phi = phi i32* [ %a, %entry ], [ %arrayidx.inc, %for.body ]
   %i.02 = phi i32 [ 0, %entry ], [ %inc, %for.body ]