[llvm-objcopy] Rename --keep to --keep-section.

Summary:
llvm-objcopy/strip support `--keep` (for sections) and `--keep-symbols` (for symbols). For consistency and clarity, rename `--keep` to `--keep-section`.
In fact, for GNU compatability, -K is --keep-symbol, so it's weird that the alias `-K` is not the same as the short-ish `--keep`.

Reviewers: jakehehrlich, jhenderson, alexshap, MaskRay, espindola

Reviewed By: jakehehrlich, MaskRay

Subscribers: emaste, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D54477

llvm-svn: 346782
diff --git a/llvm/test/tools/llvm-symbolizer/split-debug.test b/llvm/test/tools/llvm-symbolizer/split-debug.test
index 2d5b073..7474cd6 100644
--- a/llvm/test/tools/llvm-symbolizer/split-debug.test
+++ b/llvm/test/tools/llvm-symbolizer/split-debug.test
@@ -18,7 +18,7 @@
 #Build as : clang -g -O2 addr.c
 
 RUN: mkdir -p %t/.debug
-RUN: llvm-objcopy --keep=.debug_info %p/Inputs/addr.exe %t/.debug/addr
+RUN: llvm-objcopy --keep-section=.debug_info %p/Inputs/addr.exe %t/.debug/addr
 RUN: llvm-objcopy --strip-debug --add-gnu-debuglink=%t/.debug/addr %p/Inputs/addr.exe %t/addr.exe
 RUN: llvm-symbolizer -print-address -obj=%t/addr.exe < %p/Inputs/addr.inp | FileCheck %s