configure doesn't properly detect jdk while execute with "--enable-javacashlib"

[sickpig]

if you rung configure like that:

./configure --enable-shared --enable-javacashlib

and you don't have java (jdk) installed in your system you are going to get this error during the make step:

  CXX      crypto/libbitcoincash_la-aes.lo
  CXX      crypto/libbitcoincash_la-chacha20.lo
../../src/cashlib/cashlib.cpp:548:10: fatal error: jni.h: No such file or directory
 #include <jni.h>
          ^~~~~~~

it seems to me then that configure doesn't properly detect jdk

[sickpig]

setting JAVA_HOME env var before compilation fixed the problem, but indeed this is just a workaround

export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64