[llvm-exegis][test] Ignore file path in no-aliasing-ld-str.s

This test failed on a buildbot where the path happened to contain
"ld2":
/home/b/sanitizer-aarch64-linux-bootstrap-hwasan/build/llvm_build2_hwasan/test/tools/llvm-exegesis/AArch64/Output/no-aliasing-ld-str.s.tmp.obj: file format elf64-littleaarch64

To fix this, make lit consume a line past this one and
do the check-not after that point.

Author: DavidSpickett

llvm/test/tools/llvm-exegesis/AArch64/no-aliasing-ld-str.s

@@ -4,5 +4,7 @@ RUN: llvm-exegesis -mtriple=aarch64 -mcpu=neoverse-v2 -mode=latency --dump-objec
 RUN: llvm-objdump -d %t.obj > %t.s
 RUN: FileCheck %s < %t.s
 
+// Start matching after the printed file path, as that may contain something that looks like a mnemonic.
+CHECK: Disassembly of section .text:
 CHECK-NOT: ld{{[1-4]}}
 CHECK-NOT: st{{[1-4]}}