[test] Add '-o -' to llc command to avoid creating unnecessary temp files

Author: gribozavr

llvm/test/tools/llc/new-pm/x86_64-regalloc-pipeline.mir

@@ -1,6 +1,6 @@
 # REQUIRES x86_64-registered-target
-# RUN: llc -mtriple=x86_64-unknown-linux-gnu -enable-new-pm -O3 -regalloc-npm=fast -print-pipeline-passes %s 2>&1 | FileCheck %s
-# RUN: llc -mtriple=x86_64-unknown-linux-gnu -enable-new-pm -O3 -regalloc-npm=greedy -print-pipeline-passes %s 2>&1 | FileCheck %s --check-prefix=CHECK-GREEDY
+# RUN: llc -mtriple=x86_64-unknown-linux-gnu -enable-new-pm -O3 -regalloc-npm=fast -print-pipeline-passes %s -o - 2>&1 | FileCheck %s
+# RUN: llc -mtriple=x86_64-unknown-linux-gnu -enable-new-pm -O3 -regalloc-npm=greedy -print-pipeline-passes %s -o - 2>&1 | FileCheck %s --check-prefix=CHECK-GREEDY
 
 # CHECK: regallocfast
 # CHECK-GREEDY: greedy<all>