source file '<filename>' ignored
The CL.EXE did not take the source file <filename> as an input file.
This happens, for example, if you inadvertently include a space between the /Fo option and an output filename on a command line with the /c option. In the following command line, CL.EXE would take output.obj as the name of an input file because there is a space between /Fo and output.obj:
cl /c /Fo output.obj input.c
In this case, the fix is to remove the space, thus:
cl /c /Fooutput.obj input.c