Revert [llvm-objcopy][NFCI] Fix build failure with GCC

This reverts r364263 (git commit 81eb82840524818ec0ec14285c866c09b9634df0)

This commit is related to r364254 which is causing some llvm-objcopy tests
to fail with valgrind.

Error:
Conditional jump or move depends on uninitialised value(s)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364378 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-objcopy/llvm-objcopy.cpp

@@ -150,8 +150,6 @@ static Error executeObjcopyOnRawBinary(const CopyConfig &Config,
   case FileFormat::Unspecified:
     return elf::executeObjcopyOnRawBinary(Config, In, Out);
   }
-
-  llvm_unreachable("unsupported output format");
 }
 
 /// The function executeObjcopyOnBinary does the dispatch based on the format