Environment Variable for DOT path in Doxygen for Windows

We had a similar issue recently for PLANTUML with doxygen, see below for a solution.

In the configuration file (Doxyfile) checked in, use an environment variable, as in:

PLANTUML_JAR_PATH      = $(PLANTUML_JAR_PATH)

In each developer environment, define the variable with the proper path, depending on platform and specific machines.

In my case for linux, for example:

malff@linux-8edv:GIT_TRUNK> uname -a
Linux linux-8edv 4.1.39-53-default #1 SMP PREEMPT Thu Mar 30 06:44:23 UTC 2017 (56cc5a0) x86_64 x86_64 x86_64 GNU/Linux
malff@linux-8edv:GIT_TRUNK> env | grep PLANTUML_JAR_PATH
PLANTUML_JAR_PATH=/home/malff/plantuml/plantuml.8053.jar

Not tested, but I think something similar should work for DOT_PATH.