[WebAssembly] __has_attribute(musttail) evaluates to true even when musttail is unsupported #163256
Description
$ cat test.cpp
#if __has_attribute(musttail) #warning HAS IT #else #warning DOES NOT HAVE #endif void F(void) { [[clang::musttail]] return F(); }$ clang++ -std=c++20 -target wasm32-unknown-unknown -c test.cpp test.cpp:2:2: warning: HAS IT [-W#warnings] 2 | #warning HAS IT | ^ test.cpp:6:6: error: WebAssembly 'tail-call' feature not enabled 6 | void F(void) { [[clang::musttail]] return F(); } | ^ 1 warning and 1 error generated.