As they write here , msdev.exe is the name of the executable IDE VC6 file, and starting with VS2003 the file is called devenv.exe (or VCExpress.exe in express versions).
By the way, if you open Makefile.win , you can find the following comments there:
# You can override the build mechanism, choose only one; # # USEMAK=1 - compile from exported make files # USEDSW=1 - compile from .dsw / .dsp VC6 projects # USESLN=1 - compile from converted .sln / .vcproj VC7+ files
and further, there is an automatic determination of which build system to use. And judging by the fact that apr.dsw and apr.dsp files are present in the apr repo, by default it is assumed that the assembly will be done in VC6 .