Assume $FRAMEWORKSHOME/JavaVM/Headers is junk

(What I have on OS X 10.9 $FRAMEWORKSHOME/JavaVM.framework/Headers, but that
should already be covered by the preceding
$FRAMEWORKSHOME/JavaVM.framework/Versions/Current/Headers.)

Also, fix up 359ba1dfdf8de1f2cff185f16ec21b6dc88feac9 "OS X: JDK include path
for JDK 1.8" to not set JAVAINC twice.

Change-Id: I83c0cdc33ada897fcf8b79fb8df737af26687aa6
Reviewed-on: https://gerrit.libreoffice.org/9931
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>