Fix silent test failures on windows

[tristanlabelle]

The build was succeeding after test failures because exit /b from within a call only exits the subroutine, not the full script:

IF "%SKIP_TEST%"=="0" call :TestSwift

cmake --build %BuildRoot%\1 --target check-swift || (exit /b)

We need to also bubble the error after the call returns.

[bnbarham]

@swift-ci please test

[bnbarham]

Is this also happening on main then 🤔?

[bnbarham]

swift-ci@EC2AMAZ-JCVOGM7 C:\Users\swift-ci\jenkins\workspace\swift-PR-windows>move T:\package\toolchain\toolchain.msi T:\package   || (exit /b ) 
The system cannot find the file specified.

[bnbarham]

I've included in #68692. @tristanlabelle could you put this up on main 🙏?

[compnerd]

@bnbarham the MSI restructuring on main would explain why toolchain.msi is not found on main.

[compnerd]

@swift-ci please build toolchain Windows platform

[bnbarham]

I've cherry-picked this to the other 5.9 branch anyway @compnerd. Can close this one.

[tristanlabelle]

@bnbarham main already has this, albeit in a slightly different form:

I will close this in favor of #68692, and I can help look into the missing msi.