give test fn a more descriptive name

Author: GYT

llvm/test/Transforms/LoopVectorize/diag-disabled-vectorization-msgs.ll

@@ -43,7 +43,7 @@
 ; FORCEDONLY-SAME: loop not vectorized: only vectorizing loops that explicitly request it
 ; FORCEDONLY: LV: Loop hints prevent vectorization
 
-define double @CompareDistmats(ptr %distmat1){
+define double @disabled_loop_vectorization(ptr %distmat1){
 entry:
   br label %for.body