32-bit mongod.exe built from the master branch is no longer compatible with Windows XP.

The problematic revision is 15d5ed, which introduces support for ProcessInfo::blockInMemory on Windows. Unfortunately, it relies on QueryWorkingSetEx, which is not available on 32-bit Windows XP. My understanding is that it is, however, available on 64-bit Windows XP as well as all editions of Windows Vista and Windows Server 2003 and above.

Did you intentionally introduce this incompatibility?

To retain compatibility with 32-bit Windows XP while retaining the new feature, I believe it would be necessary to load psapi.dll dynamically, and to return true from ProcessInfo::blockCheckSupported only if QueryWorkingSetEx is available.