JCC’s setup.py file needs to be edited before building JCC to specify the location of the Java Runtime Environment’s header files and libraries.
However, it appears you have a better mechanism of setting JCC_JDK, but it's not documented.
Second, when setting JCC_JDK is appears to work correctly and use the path to the specified JCC_JDK in the compilation, but the first line of output might indicate that a different JRE is being used:
So maybe the found JAVAHOME should not be printed if JCC_JDK is set, so it appears that JCC_JDK is successfully overriding the JAVAHOME. I'll attach the full output from building on my platform.