[llvm-strip] Expose --keep-symbol option

Expose --keep-symbol option in llvm-strip.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D47222

llvm-svn: 333117
diff --git a/llvm/tools/llvm-objcopy/StripOpts.td b/llvm/tools/llvm-objcopy/StripOpts.td
index 1d7a1ae..7c8862f 100644
--- a/llvm/tools/llvm-objcopy/StripOpts.td
+++ b/llvm/tools/llvm-objcopy/StripOpts.td
@@ -16,3 +16,10 @@
 
 def R : JoinedOrSeparate<["-"], "R">,
         Alias<remove_section>;
+
+defm keep_symbol : Eq<"keep-symbol">,
+                   MetaVarName<"symbol">,
+                   HelpText<"Do not remove symbol <symbol>">;
+
+def K : JoinedOrSeparate<["-"], "K">,
+        Alias<keep_symbol>;
diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
index dbe8f8c..6aac11a 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -557,6 +557,9 @@
 
   for (auto Arg : InputArgs.filtered(STRIP_remove_section))
     Config.ToRemove.push_back(Arg->getValue());
+  
+  for (auto Arg : InputArgs.filtered(STRIP_keep_symbol))
+    Config.SymbolsToKeep.push_back(Arg->getValue());
 
   return Config;
 }