[llvm-strip] Add --keep-file-symbols

[jhenderson]

LGTM.

test/tools/llvm-objcopy/ELF/keep-file-symbols.test

 # RUN: yaml2obj %s > %t
 # RUN: llvm-objcopy --strip-all --keep-file-symbols %t %t2
 # RUN: llvm-readobj --symbols %t2 | FileCheck %s --check-prefix=STRIPALL
 # RUN: llvm-objcopy --keep-file-symbols --strip-symbol foo %t %t2
 # RUN: llvm-readobj --symbols %t2 | FileCheck %s --check-prefix=STRIP
 
+# RUN: llvm-strip --keep-file-symbols %t -o %t3
+# RUN: llvm-readobj --symbols %t3 | FileCheck %s --check-prefix=STRIPALL
+# RUN: llvm-strip --keep-file-symbols --strip-symbol foo %t -o %t4
+# RUN: llvm-readobj --symbols %t4 | FileCheck %s --check-prefix=STRIP
+
 !ELF
 FileHeader:
   Class:           ELFCLASS64
   Data:            ELFDATA2LSB
   Type:            ET_REL
   Machine:         EM_X86_64
 Sections:
   - Name:            .text

tools/llvm-objcopy/CopyConfig.cpp

DriverConfig parseStripOptions(ArrayRef<const char *> ArgsArr) {
   if (InputArgs.hasArg(STRIP_discard_all, STRIP_discard_locals))
     Config.DiscardMode =
         InputArgs.hasFlag(STRIP_discard_all, STRIP_discard_locals)
             ? DiscardType::All
             : DiscardType::Locals;
   Config.StripUnneeded = InputArgs.hasArg(STRIP_strip_unneeded);
   Config.StripAll = InputArgs.hasArg(STRIP_strip_all);
   Config.StripAllGNU = InputArgs.hasArg(STRIP_strip_all_gnu);
+  Config.KeepFileSymbols = InputArgs.hasArg(STRIP_keep_file_symbols);
 
   for (auto Arg : InputArgs.filtered(STRIP_keep_section))
     Config.KeepSection.push_back(Arg->getValue());
 
   for (auto Arg : InputArgs.filtered(STRIP_remove_section))
     Config.ToRemove.push_back(Arg->getValue());
 
   for (auto Arg : InputArgs.filtered(STRIP_strip_symbol))

tools/llvm-objcopy/StripOpts.td

 defm strip_symbol : Eq<"strip-symbol", "Strip <symbol>">,
                     MetaVarName<"symbol">;
 def N : JoinedOrSeparate<["-"], "N">, Alias<strip_symbol>;
 
 defm keep_section : Eq<"keep-section", "Keep <section>">,
                     MetaVarName<"section">;
 defm keep_symbol : Eq<"keep-symbol", "Do not remove symbol <symbol>">,
                    MetaVarName<"symbol">;
+def keep_file_symbols : Flag<["-", "--"], "keep-file-symbols">,
+                        HelpText<"Do not remove file symbols">;
+
 def K : JoinedOrSeparate<["-"], "K">, Alias<keep_symbol>;
 
 def discard_locals : Flag<["-", "--"], "discard-locals">,
                      HelpText<"Remove compiler-generated local symbols, (e.g. "
                               "symbols starting with .L)">;
 def X : Flag<["-"], "X">, Alias<discard_locals>;
 
 def discard_all
     : Flag<["-", "--"], "discard-all">,
       HelpText<"Remove all local symbols except file and section symbols">;
 def x : Flag<["-"], "x">, Alias<discard_all>;
 
 def version : Flag<["-", "--"], "version">,
               HelpText<"Print the version and exit.">;
 def V : Flag<["-"], "V">, Alias<version>;