[native_toolchain_c] Clang resolver trips over symlink to llvm executable

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 --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.