Gentoo's Bugzilla –
Attachment 508754 Details for
Bug 640214app-emulation/virtualbox-5.1.30::gentoo: /var/tmp/portage/app-emulation/virtualbox-5.1.30/work/VirtualBox-5.1.30/src/libs/xpcom18a4/java/src/nsAppFileLocProviderProxy.h:42:17: fatal error: jni.h: No such file or directory