Report original emulation name in "unknown emulation" error

[emaste]

Summary

We strip a trailing _fbsd from emulation names, but if the result is not a valid emulation the error was somewhat confusing:

% ld.lld -m elf_amd64_fbsd
unknown emulation: elf_amd64

Use the unmodified emulation name in error messages.

[davide]

This is OK too. Please wait on Rui on this one as he might have some opinions on the variable name.
FWIW, Emul is fine by me.

[davide]

Also, do you mind to add a test that exercises the following behaviour?

[ruiu]

LGTM

[emaste]

Update an existing "unknown emulation" test to verify this change

lld/trunk/ELF/Driver.cpp

bool elf::link(ArrayRef<const char *> Args, raw_ostream &Error) {
   Driver = &D;
   ScriptConfig = &SC;
 
   Driver->main(Args);
   return !HasError;
 }
 
 // Parses a linker -m option.
-static std::pair<ELFKind, uint16_t> parseEmulation(StringRef S) {
+static std::pair<ELFKind, uint16_t> parseEmulation(StringRef Emul) {
+  StringRef S = Emul;
   if (S.endswith("_fbsd"))
     S = S.drop_back(5);
 
   std::pair<ELFKind, uint16_t> Ret =
       StringSwitch<std::pair<ELFKind, uint16_t>>(S)
           .Case("aarch64elf", {ELF64LEKind, EM_AARCH64})
           .Case("aarch64linux", {ELF64LEKind, EM_AARCH64})
           .Case("armelf_linux_eabi", {ELF32LEKind, EM_ARM})
           .Case("elf32_x86_64", {ELF32LEKind, EM_X86_64})
           .Case("elf32btsmip", {ELF32BEKind, EM_MIPS})
           .Case("elf32ltsmip", {ELF32LEKind, EM_MIPS})
           .Case("elf32ppc", {ELF32BEKind, EM_PPC})
           .Case("elf64btsmip", {ELF64BEKind, EM_MIPS})
           .Case("elf64ltsmip", {ELF64LEKind, EM_MIPS})
           .Case("elf64ppc", {ELF64BEKind, EM_PPC64})
           .Case("elf_amd64", {ELF64LEKind, EM_X86_64})
           .Case("elf_i386", {ELF32LEKind, EM_386})
           .Case("elf_iamcu", {ELF32LEKind, EM_IAMCU})
           .Case("elf_x86_64", {ELF64LEKind, EM_X86_64})
           .Default({ELFNoneKind, EM_NONE});
 
   if (Ret.first == ELFNoneKind) {
     if (S == "i386pe" || S == "i386pep" || S == "thumb2pe")
-      error("Windows targets are not supported on the ELF frontend: " + S);
+      error("Windows targets are not supported on the ELF frontend: " + Emul);
     else
-      error("unknown emulation: " + S);
+      error("unknown emulation: " + Emul);
   }
   return Ret;
 }
 
 // Returns slices of MB by parsing MB as an archive file.
 // Each slice consists of a member file in the archive.
 std::vector<MemoryBufferRef>
 LinkerDriver::getArchiveMembers(MemoryBufferRef MB) {

lld/trunk/test/ELF/basic.s

 
 # RUN: not ld.lld --foo 2>&1 | FileCheck --check-prefix=UNKNOWN %s
 # UNKNOWN: unknown argument: --foo
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 # RUN: not ld.lld %t %t -o %t2 2>&1 | FileCheck --check-prefix=DUP %s
 # DUP: duplicate symbol: _start in {{.*}} and {{.*}}
 
-# RUN: not ld.lld %t -o %t -m wrong_emul 2>&1 | FileCheck --check-prefix=UNKNOWN_EMUL %s
-# UNKNOWN_EMUL: unknown emulation: wrong_emul
+# RUN: not ld.lld %t -o %t -m wrong_emul_fbsd 2>&1 | FileCheck --check-prefix=UNKNOWN_EMUL %s
+# UNKNOWN_EMUL: unknown emulation: wrong_emul_fbsd
 
 # RUN: not ld.lld %t --lto-jobs=0 2>&1 | FileCheck --check-prefix=NOTHREADS %s
 # NOTHREADS: number of threads must be > 0