[llvm-objcopy][test] Stablize build-id-link-dir.test

Author: MaskRay

llvm/test/tools/llvm-objcopy/ELF/build-id-link-dir.test

@@ -1,5 +1,5 @@
 # RUN: yaml2obj %s -o %t
-# RUN: mkdir -p %t-dir
+# RUN: rm -fr %t-dir && mkdir %t-dir
 
 # RUN: llvm-objcopy --build-id-link-dir=%t-dir %t %t2
 # RUN: not test -e %t-dir/4f/cb712aa6387724a9f465a32cd8c14b