[native_toolchain_c] Clang resolver trips over symlink to llvm executable

[dcharkes]

Apparently, newer clang versions all symlink to llvm, but then need to be invoked with llvm clang.

dacoharkes@dacoharkes-linux:~/dart-sdk/sdk/buildtools/linux-x64/clang/bin$ ls -lah clang
lrwxrwxrwx 1 dacoharkes primarygroup 4 Aug 23 15:10 clang -> llvm
dacoharkes@dacoharkes-linux:~/dart-sdk/sdk/buildtools/linux-x64/clang/bin$ ./llvm --version
OVERVIEW: llvm toolchain driver

USAGE: llvm [subcommand] [options]

SUBCOMMANDS:

  size
  readobj
  readelf
  rc
  windres
  profdata
  objcopy
  install-name-tool
  bitcode-strip
  strip
  nm
  mt
  lipo
  ifs
  gsymutil
  cxxfilt
  ar
  ranlib
  lib
  dlltool
  lld
  lld-link
  ld.lld
  ld64.lld
  wasm-ld
  clang-scan-deps
  clang
  clang++
  clang-cl
  clang-cpp

  Type "llvm <subcommand> --help" to get more help on a specific subcommand

OPTIONS:

  --help - Display this message

dacoharkes@dacoharkes-linux:~/dart-sdk/sdk/buildtools/linux-x64/clang/bin$ clang --version
Debian clang version 14.0.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

dacoharkes@dacoharkes-linux:~/dart-sdk/sdk/buildtools/linux-x64/clang/bin$ ls -lah ld.lld
lrwxrwxrwx 1 dacoharkes primarygroup 4 Aug 23 15:10 ld.lld -> llvm

Currently our logic fails, because it follows symlinks from clang to llvm and then fails to invoke llvm with a clang sub command.

In our tools abstraction, a tool instance refers to an executable, so having the linker/archiver/compiler all refer to the llvm executable is slightly weird, maybe we should have a new llvm tool/toolinstances to model this correctly.

The subcommand executables are still there, so as a stopgap we can probably stop following symlinks for LLVM for now.