title: "Missing" jni.h File Causes JPostal Build to Fail
body: <p>I'm trying <a href="https://github.com/openvenues/jpostal#building-jpostal" rel="nofollow noreferrer">to build JPostal</a> but I get the following error after issuing the command <code>./gradlew assemble</code>:</p>
  <pre><code>checking for gcj... no
  checking for guavac... no
  checking for jikes... no
  checking for javac... javac
  checking if javac works... yes
  checking for C:\x\Java\jdk1.8.0_191/include/jni.h... yes
  checking for stdlib.h... (cached) yes
  checking for string.h... (cached) yes
  checking for size_t... yes
  checking for uint16_t... yes
  checking for GNU libc compatible malloc... yes
  checking for strdup... yes
  checking for pkg-config... /usr/bin/pkg-config
  checking pkg-config is at least version 0.9.0... yes
  checking for LIBPOSTAL... yes
  checking that generated files are newer than configure... done
  configure: creating ./config.status
  config.status: creating Makefile
  config.status: creating src/main/c/Makefile
  config.status: creating config.h
  config.status: executing depfiles commands
  config.status: executing libtool commands
  </code></pre>
  <hr />
  <pre><code>Making install in src/main/c
  make[1]: Entering directory '/c/x/ProgramFiles/JPostal/src/main/c'
  /bin/sh ../../../libtool  --tag=CC   --mode=compile gcc -DHAVE_CONFIG_H -I. -I../../..     -g -O2 -IC:\x\Java\jdk1.8.0_191/include -MT libjpostal_parser_la-jpostal_AddressParser.lo -MD -MP -MF .deps/libjpostal_parser_la-jpostal_AddressParser.Tpo -c -o libjpostal_parser_la-jpostal_AddressParser.lo `test -f 'jpostal_AddressParser.c' || echo './'`jpostal_AddressParser.c
  libtool: compile:  gcc -DHAVE_CONFIG_H -I. -I../../.. -g -O2 -IC:xJavajdk1.8.0_191/include -MT libjpostal_parser_la-jpostal_AddressParser.lo -MD -MP -MF .deps/libjpostal_parser_la-jpostal_AddressParser.Tpo -c jpostal_AddressParser.c  -DDLL_EXPORT -DPIC -o .libs/libjpostal_parser_la-jpostal_AddressParser.o
  jpostal_AddressParser.c:1:10: fatal error: jni.h: No such file or directory
      1 | #include &lt;jni.h&gt;
        |          ^~~~~~~
  compilation terminated.
  make[1]: *** [Makefile:473: libjpostal_parser_la-jpostal_AddressParser.lo] Error 1
  make[1]: Leaving directory '/c/x/ProgramFiles/JPostal/src/main/c'
  make: *** [Makefile:404: install-recursive] Error 1
  :buildJniLib FAILED
  
  FAILURE: Build failed with an exception.
  
  * What went wrong:
  Execution failed for task ':buildJniLib'.
  &gt; Process 'command 'sh'' finished with non-zero exit value 2
  
  * Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.
  
  BUILD FAILED
  
  Total time: 58.914 secs
  </code></pre>
  <p>I installed LibPostal exactly as described <a href="https://github.com/openvenues/libpostal" rel="nofollow noreferrer">here</a> so why are the file <code>jni.h</code>, <code>gcj</code>, <code>guavac</code> and <code>jikes</code> libs missing?</p>
  <p>I looked at GitHub and I didn't see any <a href="https://github.com/openvenues/jpostal/issues" rel="nofollow noreferrer">open issues</a> addressing this question.</p>
  <p><strong>UPDATE 1</strong>:</p>
  <p>In the screenshot below you can see that the <code>jni.h' file is clearly present in </code>/include/` folder:</p>
  <p><a href="https://i.stack.imgur.com/9QcA4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9QcA4.jpg" alt="enter image description here" /></a></p>