MSFT: 59434158 - WME ADO builds are hanging in SetUpFFmpegBuildEnvironment.ps1 while trying to update MSYS2 packages via pacman (#335)

## Why is this change being made?
WME ADO builds are sporadically hanging in SetUpFFmpegBuildEnvironment.ps1 while trying to update MSYS2 packages via pacman. This issue has also been reported by #324.

I'm not able to repro the hang locally on my dev machine, and I haven't been able to root cause the hang or find a workaround for the WME ADO build.

## What changed?
I disabled MSYS2 package updates via pacman in SetUpFFmpegBuildEnvironment.ps1 until the sporadic hang can be mitigated.

## How was the change tested?
I verified that WME ADO builds run successfully.

Author: brbeec

SetUpFFmpegBuildEnvironment.ps1

@@ -72,12 +72,17 @@ $msys2_shell = "$msys2_root\msys2_shell.cmd"
 Write-Host "Modifying $msys2_shell..."
 (Get-Content $msys2_shell).replace('rem set MSYS2_PATH_TYPE=inherit', 'set MSYS2_PATH_TYPE=inherit') | Set-Content $msys2_shell
 
-# Update packages
+<# TODO: pacman sporadically hangs while updating packages
+# Update packages - the first pass updates core packages and the second pass updates the remaining non-core packages
 Write-Host 'Updating packages...'
 for ($i = 0; $i -lt 2; $i++)
 {
+    # Close all MSYS2 processes
+    & taskkill /FI 'MODULES eq msys-2.0.dll' /F | Out-Null
+
     Start-Process -Wait $msys2_shell -ArgumentList '-c "pacman -Syuu --noconfirm"'
 }
+#>
 
 # Install additional packages 
 $packages = @('make', 'gcc', 'diffutils', 'nasm')