[llvm-objcopy] Tidy up error messages

This patch brings various error messages into line with each other, by
removing trailing full stops, and making the first letter lower-case.
This addresses https://bugs.llvm.org/show_bug.cgi?id=40859.

Reviewed by: jhenderson, rupprecht, jakehehrlich

Differential Revision: https://reviews.llvm.org/D62072

Patch by Alex Brachet

llvm-svn: 361384
diff --git a/llvm/tools/llvm-objcopy/COFF/Object.cpp b/llvm/tools/llvm-objcopy/COFF/Object.cpp
index 0ad5a05..b07532c 100644
--- a/llvm/tools/llvm-objcopy/COFF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/COFF/Object.cpp
@@ -53,7 +53,7 @@
       auto It = SymbolMap.find(R.Target);
       if (It == SymbolMap.end())
         return createStringError(object_error::invalid_symbol_index,
-                                 "Relocation target %zu not found", R.Target);
+                                 "relocation target %zu not found", R.Target);
       It->second->Referenced = true;
     }
   }