windows10 64 bit ldc2 / dub issue

[Carl Sturtivant]

Today just moved from a working ldc2 1.8.0 to 1.9.0 by simply 
changing my PATH. After that a freshly made default hello world 
vibe.d application does not build.

A simple hello.d builds and runs fine using ldc2 1.9.0 directly 
i.e. without dub.

dub init hello --type=vibe.d
cd hello
dub --force

The above builds all vibe.d libraries fine, then when building 
the application I get:

Warning: no Visual C++ installation detected
C:\Users\carl\ldc2-1.9.0-windows-x64\bin\ldc2.exe failed with 
exit code 1.

and then no further information.

The selfsame warning also occurred when building with ldc2 1.8.0 
(and 1.4.0 prior to that, all on the same machine) but the 
failure does not occur and the resulting application runs fine.

Also, when building a simple hello.d without dub, which works 
fine, there is no warning "no Visual C++ installation detected". 
This warning only appears with dub and not with direct use of the 
compiler with all choices of ldc2: 1.4.0, 1.8.0, 1.9.0.

ldc2 1.10.0 behaves the same as 1.9.0 in the above situations.

I am using the stand-alone Visual C++ Build Tools as described 
here:
https://github.com/ldc-developers/ldc#windows
and this has worked fine for me with ldc2 until now. I simply ran 
the installer for those long ago, and did nothing further.

Any suggestions?