[llvm-objcopy][docs] Add missing options to the help output and the command guide

This change is to keep the help text and command guide of objcopy in
tandem.

- In the help output the options --rename-section and
  --set-section-flags were missing the flag exclude, which is found in
  the command guide.
- In the command guide the alias -G for --keep-global-symbol was
    missing, which is found in the help output.

Differential Revision: https://reviews.llvm.org/D110340

Author: gbreynoo

llvm/docs/CommandGuide/llvm-objcopy.rst

@@ -338,7 +338,7 @@ them.
 
  Keep symbols of type `STT_FILE`, even if they would otherwise be stripped.
 
-.. option:: --keep-global-symbol <symbol>
+.. option:: --keep-global-symbol <symbol>, -G
 
  Make all symbols local in the output, except for symbols with the name
  ``<symbol>``. Can be specified multiple times to ignore multiple symbols.

llvm/tools/llvm-objcopy/ObjcopyOpts.td

@@ -50,7 +50,8 @@ defm rename_section
     : Eq<"rename-section",
          "Renames a section from old to new, optionally with specified flags. "
          "Flags supported for GNU compatibility: alloc, load, noload, "
-         "readonly, debug, code, data, rom, share, contents, merge, strings.">,
+         "readonly, exclude, debug, code, data, rom, share, contents, merge, "
+         "strings.">,
       MetaVarName<"old=new[,flag1,...]">;
 defm redefine_symbol
     : Eq<"redefine-sym", "Change the name of a symbol old to new">,
@@ -82,8 +83,8 @@ defm set_section_alignment
 defm set_section_flags
     : Eq<"set-section-flags",
          "Set section flags for a given section. Flags supported for GNU "
-         "compatibility: alloc, load, noload, readonly, debug, code, data, "
-         "rom, share, contents, merge, strings.">,
+         "compatibility: alloc, load, noload, readonly, exclude, debug, code, "
+         "data, rom, share, contents, merge, strings.">,
       MetaVarName<"section=flag1[,flag2,...]">;
 
 def S : Flag<["-"], "S">,