if is not a program but a shell (cmd) builtin, so invoke the shell. 
clean:
    -cmd /c if exist glversion.txt del glversion.txt
    -cmd /c if exist glversion.exe del glversion.exe
    -cmd /c if exist glversion.o   del glversion.o

[download]

By the way, I fixed the file name in the last one.

In reply to Re: [OT] Makefiles - nmake syntax v dmake syntax by ikegami
in thread [OT] Makefiles - nmake syntax v dmake syntax by syphilis

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