[ELF] Add some arm and aarch64 emulation modes, recognized by ld

[evgeny777]

Summary

Required to build our projects

[ruiu]

Did you verify that all of them are actually in use? I'd like to add strings that we have to add.

[evgeny777]

Okay, for now I need aarch64elf. Is it okay to add just that?

[ruiu]

Sure.

[emaste]

For FreeBSD it looks like we use "aarch64fbsd", but we can add it later if/when necessary

ELF/Driver.cpp

 
 // Parses a linker -m option.
 static std::pair<ELFKind, uint16_t> parseEmulation(StringRef S) {
   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("aarch64elfb", {ELF64BEKind, EM_AARCH64})
+          .Case("aarch64elf32", {ELF32LEKind, EM_AARCH64})
+          .Case("aarch64elf32b", {ELF32BEKind, EM_AARCH64})
+          .Case("aarch64linux32", {ELF32LEKind, EM_AARCH64})
+          .Case("aarch64linux32b", {ELF32BEKind, EM_AARCH64})
           .Case("aarch64linux", {ELF64LEKind, EM_AARCH64})
+          .Case("aarch64linuxb", {ELF64BEKind, EM_AARCH64})
+          .Case("armelf", {ELF32LEKind, EM_ARM})
+          .Case("armelfb", {ELF32BEKind, EM_ARM})
           .Case("armelf_linux_eabi", {ELF32LEKind, EM_ARM})
+          .Case("armelfb_linux_eabi", {ELF32BEKind, 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_i386", {ELF32LEKind, EM_386})