Fix a compile error by using clang-x86_64-pc-windows-msvc

[kkitayam]

Fix compile errors when using clang-x86_64-pc-windows-msvc

Please see also raspberrypi/picotool#129

• Environment

$ clang --version
clang version 18.1.8
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin
Error messages

• An error message

C:/hoge/pico-sdk/src/host/pico_platform/include\pico/platform.h:99:24: error: definition of builtin function '__builtin_unreachable'
   99 | static __noreturn void __builtin_unreachable() {
      |                        ^
1 error generated.

[kilograham]

did you mean if !defined(_MSC_VER) && !defined(__clang__)?

[kkitayam]

No, it's not. The changes were intended to disable LL.74-103 when using clang-x86_64-pc-windows-msvc.

clang-x86_64-pc-windows-msvc has built-in functions like gcc syntax. Specifically there are __builtin_unreachable and __builtin_clz. Also, clang-x86_64-pc-windows-msvc has a macro _MSC_VER already defined. So, LL.74-103 were enabled. As a result, the compilation fails.