🌲Disable strict preprocessor on Windows

[etcwilde]

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The Windows SDK on CI is not compliant, so enabling strict preprocessor mode is resulting in build failures in headers in the SDK itself. This is preventing actionable progress on rebranch, so disabling until we have a newer Windows SDK that is compliant.

Radar tracking updating the SDK: rdar://113996252 We should re-enable the strict preprocessing once that task is completed.

Failures we hope to get past:

16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\oaidl.h(487): warning C5103: pasting '/' and '/' does not result in a valid preprocessing token
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\shared\wtypes.h(745): note: in expansion of macro '_VARIANT_BOOL'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\oaidl.h(487): error C2059: syntax error: '/'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\oaidl.h(487): error C2238: unexpected token(s) preceding ';'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\oaidl.h(502): warning C5103: pasting '/' and '/' does not result in a valid preprocessing token
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\shared\wtypes.h(745): note: in expansion of macro '_VARIANT_BOOL'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\oaidl.h(502): error C2059: syntax error: '/'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\oaidl.h(502): error C2238: unexpected token(s) preceding ';'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\propidlbase.h(319): warning C5103: pasting '/' and '/' does not result in a valid preprocessing token
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\shared\wtypes.h(745): note: in expansion of macro '_VARIANT_BOOL'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\propidlbase.h(319): error C2059: syntax error: '/'
16:43:57 C:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um\propidlbase.h(319): error C2238: unexpected token(s) preceding ';

[etcwilde]

@swift-ci please test Windows

[compnerd]

lib\ExecutionEngine\JITLink\COFFOptions.inc(42): note: see declaration of 'llvm::jitlink::COFF_OPT_'

not sure if this is related to the change