I run MSys/Bash as distributed in Git for Windows. I added the folder C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319 to my path, so I could run msbuild
C:\\Windows\\Microsoft.NET\\Framework\\v4.0.30319
msbuild
It's a bug in MSys where the same name is shared by a folder and a file (minus the extension). In this case:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe
C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild
You'll have to workaround by writing msbuild.exe
msbuild.exe