Windows: reenable unit tests (#33385)

Unit tests on Windows are supposed to pass for any PR to pass CI.
However, the return code for the unit test command was not being
checked, which meant this check was always passing (effectively
disabled). This PR

* Properly checks the result of the unit tests and fails if the
  unit tests fail
* Fixes (or disables on Windows) a number of tests which have
  "drifted" out of support on Windows since this check was
  effectively disabled

share/spack/qa/setup_spack.ps1

@@ -1,3 +0,0 @@
-spack compiler find
-echo F|xcopy .\spack\share\spack\qa\configuration\windows_config.yaml $env:USERPROFILE\.spack\windows\config.yaml
-spack external find cmake

share/spack/qa/setup_spack_installer.ps1

@@ -0,0 +1,2 @@
+spack compiler find
+spack external find cmake

share/spack/qa/validate_last_exit.ps1

@@ -0,0 +1,3 @@
+if ($LASTEXITCODE -ne 0){
+    throw "Unit Tests have failed"
+}

share/spack/qa/windows_test_setup.ps1

@@ -1,11 +1,5 @@
-Set-Location ../
-
-$env:python_pf_ver="C:\hostedtoolcache\windows\Python\3.9.5\x64\python.exe"
-
-cmd /c "`"spack\bin\spack_cmd.bat`" print " |
-foreach {
-    if ($_ -match "=") {
-        $v = $_.split("=")
-        [Environment]::SetEnvironmentVariable($v[0], $v[1])
-    }
-}
+$ErrorActionPreference = "SilentlyContinue"
+Write-Output F|xcopy .\share\spack\qa\configuration\windows_config.yaml $env:USERPROFILE\.spack\windows\config.yaml
+# The line below prevents the _spack_root symlink from causing issues with cyclic symlinks on Windows
+(Get-Item '.\lib\spack\docs\_spack_root').Delete()
+./share/spack/setup-env.ps1