[llvm-objcopy][NFC] Consistenly use two dashes for flags in tests.

Summary:
As pointed out in D53667, our use of hyphens in flags can be inconsistent, mixing `-` with `--`. This change makes all long style flags use `--`.

Automatically changed via:

```
find test/tools/llvm-objcopy/ELF -type f | xargs sed -i 's/ -\([a-zA-Z]\{3\}\)/ --\1/g'
```

Two false positives were manually fixed/reverted.

Reviewers: jhenderson, espindola, alexshap

Reviewed By: jhenderson

Subscribers: emaste, javed.absar, arichardson, fedor.sergeev, jakehehrlich, llvm-commits

Differential Revision: https://reviews.llvm.org/D56513

llvm-svn: 350944
diff --git a/llvm/test/tools/llvm-objcopy/ELF/segment-shift.test b/llvm/test/tools/llvm-objcopy/ELF/segment-shift.test
index 635fdcc..b4caa19 100644
--- a/llvm/test/tools/llvm-objcopy/ELF/segment-shift.test
+++ b/llvm/test/tools/llvm-objcopy/ELF/segment-shift.test
@@ -1,6 +1,6 @@
 # RUN: yaml2obj %s -o %t
 # RUN: llvm-objcopy %t %t2
-# RUN: llvm-readobj -program-headers %t2 | FileCheck %s
+# RUN: llvm-readobj --program-headers %t2 | FileCheck %s
 
 !ELF
 FileHeader: