64-bit Win 7 Professional, using default F7 debug build -- F7
Running as normal user, not admin.

3.4: built Thursday, Saturday; failed Wednesday, Friday, today Sunday.

7> cl.exe -c -D_WIN32 -DUSE_DL_EXPORT -D_WINDOWS -DWIN32 -D_WINDLL -D_DEBUG -MDd -DHGBRANCH=\"default\" -DHGTAG=\"tip\" -DHGVERSION=\"79bf4e7e4004\" ..\Modules\getbuildinfo.c -Fo"D:\Python\dev\cpython\PCbuild\Win32-temp-Debug\pythoncore\getbuildinfo.o" -I..\Include -I..\PC
7>  Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86
7>  Copyright (C) Microsoft Corporation.  All rights reserved.
7>  
7>  getbuildinfo.c
7>LINK : fatal error LNK1104: cannot open file 'D:\Python\dev\cpython\PCbuild\python34_d.dll'

I 'updated' back about 24 hours to rev 83828: worked. Forward to rev 83829: failed. This made no sense so back to '28: failed. Delete python34_d.dll: works. Update to tip: works. Try again: fails.

What I believe to be the case: if python34_d.dll is rebuilt, python_d.exe is built. If not, it 'cannot be opened' even though it is sitting there. I cannot be sure if this was always the case as I did not try to rebuild very ofter.

--
3.3 I have not been able to rebuild python_d.exe since May 7. I currently get

7>..\PC\pylauncher.rc(16): error RC2104: undefined keyword or key name: FIELD3 (for pywlauncher project)

10>..\PC\pylauncher.rc(16): error RC2104: undefined keyword or key name: FIELD3

9>..\PC\python_nt.rc(35): error RC2104: undefined keyword or key name: MS_DLL_ID (for pythoncore project)

Failure of pythoncore stops the dependent projects. I have no idea how I might work around this.