Windows keeps using MSVC, even when `CC` and `CXX` are set explicitly and empty `PATH`

nanodbc\nanodbc>set PATH="C:%HOMEPATH%\.cargo\bin"
nanodbc\nanodbc>set CC="%LIBCLANG_PATH%\clang.exe"
nanodbc\nanodbc>set CXX="%LIBCLANG_PATH%\clang++.exe"
nanodbc\nanodbc>%CC% --version
clang version 18.1.8
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin
nanodbc\nanodbc>bindgen nanodbc.h -o bindings.rs
[omitted most output for brevity]
pe '__std_exception_data'\nC:\\Program Files\\Microsoft Visual Studio\\2022\\Enterprise\\VC\\Tools\\MSVC\\14.40.33807\\include\\vcruntime_exception.h:39:13: error: must use 'struct' tag to refer to type '__std_exception_data'\nC:\\Program Files\\Microsoft Visual Studio\\2022\\Enterprise\\VC\\Tools\\MSVC\\14.40.33807\\include\\vcruntime_exception.h:45:8: error: expected identifier or '('\nC:\\Program Files\\Microsoft Visual Studio\\2022\\Enterprise\\VC\\Tools\\MSVC\\14.40.33807\\include\\exception:36:1: error: unknown type name 'namespace'\nfatal error: too many errors emitted, stopping now [-ferror-limit=]\n")

Same issue as this guy had 4 years ago #1844

Trying with the nuclear option:

:: clear all vars
nanodbc\nanodbc>for /f "usebackq delims==" %f in (`set`) do (set %f=)
nanodbc\nanodbc>set HOMEPATH :: specific to me
nanodbc\nanodbc>set LIBCLANG_PATH="C:\Program Files\LLVM\bin"
nanodbc\nanodbc>set PATH="C:%HOMEPATH%\.cargo\bin"
nanodbc\nanodbc>set CC="%LIBCLANG_PATH%\clang.exe"
nanodbc\nanodbc>set CXX="%LIBCLANG_PATH%\clang++.exe"
nanodbc\nanodbc>dir %LIBCLANG_PATH%\*clang.dll
 Volume in drive C is OS
 Volume Serial Number is D2B2-BE47

 Directory of C:\Program Files\LLVM\bin

2024-06-19  03:23 AM       100,587,008 libclang.dll
               1 File(s)    100,587,008 bytes
               0 Dir(s)  19,601,973,248 bytes free
nanodbc\nanodbc>bindgen nanodbc.h -o bindings.rs
thread 'main' panicked at C:%HOMEPATH%\.cargo\registry\src\index.crates.io-6f17d22bba15001f\bindgen-0.69.4\lib.rs:622:31:
Unable to find libclang: "couldn't find any valid shared libraries matching: ['clang.dll', 'libclang.dll'], set the `LIBCLANG_PATH` environment variable to a path where one of these files can be found (invalid: [])"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Start by reproducing the bindgen CLI invocation against nanodbc.h on Windows with CC, CXX, PATH, and LIBCLANG_PATH set as shown. Trace how bindgen discovers and invokes Clang, then verify that explicit compiler variables are honored and that the reported libclang lookup failure is resolved without relying on MSVC.