Fix D-flag.test by running chmod before creating the archive

Not all systems create the .o file with mode 644 by default.
Adding an explicit chmod invocation should fix this test added in
535b3c6b2f

llvm/test/tools/llvm-ranlib/D-flag.test

@@ -3,6 +3,7 @@
 ## Important: all `llvm-ar tv` calls must use TZ=UTC to produce identical values
 # RUN: yaml2obj %S/../llvm-ar/Inputs/add-lib1.yaml -o %t.o
 # RUN: env TZ=UTC touch -t 200001020304 %t.o
+# RUN: chmod 644 %t.o
 # RUN: rm -f %t.a %t-no-index.a && llvm-ar cqSU %t-no-index.a %t.o
 
 ## Check that the intial listing has real values: