Hi,
Normally component_compile_definitions() in the component’s file should work, so most likely the problem you are experiencing is caused by something else (e.g. source is used by a different component, or one of the CMakeLists files was overridden).
If you are not sure, please try reproducing the problem on a freshly created LEDBlink project. If it can be reproduced there, please try re-downloading the toolchain from scratch. If it still doesn’t work as expected, please check if the problem reoccurs when building the project outside VisualGDB and try submitting a bugreport to Espressif.
You can also use VisualGDB’s CMake debugger to step into the the component_compile_definitions() statement and check whether it works.