[clang] [C++20] [Modules] [Driver] Don't enable -fdelayed-template-parsing by default on windows with C++20 modules (PR #69431)

[via cfe-commits]

zeroomega wrote:

FYI, we are seeing libc++ test failures on Windows after this patch landed, for example:
llvm-libc++-static-clangcl.cfg.in :: std/numerics/c.math/cmath.pass.cpp:
```
# .---command stderr------------
# | In file included from C:\b\s\w\ir\x\w\llvm-llvm-project\libcxx\test\std\numerics\c.math\cmath.pass.cpp:11:
# | In file included from C:/b/s/w/ir/x/w/llvm_build/include/c++/v1\cmath:319:
# | In file included from C:/b/s/w/ir/x/w/llvm_build/include/c++/v1\math.h:301:
# | In file included from C:\b\s\w\ir\cache\windows_sdk\Windows Kits\10\Include\10.0.19041.0\ucrt\math.h:11:
# | C:\b\s\w\ir\cache\windows_sdk\Windows Kits\10\Include\10.0.19041.0\ucrt\corecrt_math.h:401:16: error: call to 'fpclassify' is ambiguous
# |   401 |         return fpclassify(_X) <= 0;
```
Failed build task: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-windows-x64/b8766483127060472193/overview

We will try to manually enable `-fdelayed-template-parsing` to see if it clears the error. However, these libc++ tests probably needs an update.

https://github.com/llvm/llvm-project/pull/69431