Although we knew that GDP could be built for the Renesas R-Car Gen 3 Salvator-X(S) boards they were not supported in the GDP init mechanism that sets up GDP for you. You typically asked GDP init to setup for one of the R-Car Starter Kit boards and manually made the changes to build for Salvator-X.
Between Gunnar and I we have now added Salvator-X(S) support directly into the init mechanism on the GDP master, 14.0.x-rocko and 14.1.x-sumo branches.
To initiate the build environment for M3 Salvator-X(S) use the command:
source init.sh r-car-m3-salvator-x
To initiate the build environment for H3 Salvator-X(S) use the command:
source init.sh r-car-h3-salvator-x
I have successfully tested the mechanism on M3 Salvator-X and H3 Salvator-XS.