Allow oformat option to accept elf format

[rdhindsa]

Summary

Allow oformat to accept format starting with elf as acceptable format. isOutputFormatBinary returns false in such case.
Example: --oformat elf64-x86-64

[ruiu]

lld/test/ELF/oformat-elf.s

7

I don't think you have to verify the output because -oformat elf is essentially ignored. Please add one test line like this

1. RUN: ld.lld -o /dev/null %t --oformat elf

to oformat-binary.s to verify that the command succeeds to complete.

[ruiu]

LGTM

lld/ELF/Driver.cpp

static Target2Policy getTarget2(opt::InputArgList &Args) {
   return Target2Policy::GotRel;
 }
 
 static bool isOutputFormatBinary(opt::InputArgList &Args) {
   if (auto *Arg = Args.getLastArg(OPT_oformat)) {
     StringRef S = Arg->getValue();
     if (S == "binary")
       return true;
+    if (S.startswith("elf"))
+      return false;
     error("unknown --oformat value: " + S);
   }
   return false;
 }
 
 static DiscardPolicy getDiscard(opt::InputArgList &Args) {
   if (Args.hasArg(OPT_relocatable))
     return DiscardPolicy::None;

lld/test/ELF/oformat-elf.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: ld.lld -o %t.out %t --oformat elf64-x86-64
+# RUN: od -t x1 -v %t.out | FileCheck %s
+# CHECK: 0000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
+# CHECK: 0010000 90 11 22 cc cc cc cc cc cc cc cc cc cc cc cc cc
+
+.text
+.align 4
+.globl _start
+_start:
+ nop
+
+.section        .mysec.1,"ax"
+.byte   0x11
+
+.section        .mysec.2,"ax"
+.byte   0x22