Remove "ELF Only" restriction from section flags

[rnk]

Summary

-ffunction-sections and -fdata-sections are well supported by many
object file formats:

• ELF
• COFF
• XCOFF
• wasm

Only MachO ignores this flag.

While here, remove it from -funique-section-names. Wasm honors this
option.

Addresses PR44910.

[aaron.ballman]

LGTM!

[hans]

In the commit message, which is currently "Remove "ELF Only" restriction from section flags" maybe add "help text" or something to make it obvious this only changes the help text -- i.e. it's not removing any actual "elf only" restriction.

clang/include/clang/Driver/Options.td

 
 def fwrapv : Flag<["-"], "fwrapv">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Treat signed integer overflow as two's complement">;
 def fwritable_strings : Flag<["-"], "fwritable-strings">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Store string literals as writable data">;
 def fzero_initialized_in_bss : Flag<["-"], "fzero-initialized-in-bss">, Group<f_Group>;
 def ffunction_sections : Flag<["-"], "ffunction-sections">, Group<f_Group>,
   Flags<[CC1Option]>,
-  HelpText<"Place each function in its own section (ELF Only)">;
+  HelpText<"Place each function in its own section">;
 def fno_function_sections : Flag<["-"], "fno-function-sections">, Group<f_Group>;
 def fdata_sections : Flag <["-"], "fdata-sections">, Group<f_Group>,
- Flags<[CC1Option]>, HelpText<"Place each data in its own section (ELF Only)">;
+ Flags<[CC1Option]>, HelpText<"Place each data in its own section">;
 def fno_data_sections : Flag <["-"], "fno-data-sections">, Group<f_Group>;
 def fstack_size_section : Flag<["-"], "fstack-size-section">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Emit section containing metadata on function stack sizes">;
 def fno_stack_size_section : Flag<["-"], "fno-stack-size-section">, Group<f_Group>,
   HelpText<"Don't emit section containing metadata on function stack sizes">;
 
 def funique_section_names : Flag <["-"], "funique-section-names">,
   Group<f_Group>,
-  HelpText<"Use unique names for text and data sections (ELF Only)">;
+  HelpText<"Use unique names for text and data sections">;
 def fno_unique_section_names : Flag <["-"], "fno-unique-section-names">,
   Group<f_Group>, Flags<[CC1Option]>;
 
 def fstrict_return : Flag<["-"], "fstrict-return">, Group<f_Group>,
   Flags<[CC1Option]>,
   HelpText<"Always treat control flow paths that fall off the end of a "
            "non-void function as unreachable">;
 def fno_strict_return : Flag<["-"], "fno-strict-return">, Group<f_Group>,