build: cleanup jni m4

- Don't error if not found
- Don't use AC_CHECK_FILE which is disabled on cross
- Check for darwin path

build-aux/m4/ax_jni_include_dir.m4

@@ -59,7 +59,7 @@ else
 	fi
 	AC_PATH_PROG([_ACJNI_JAVAC], [$JAVAC], [no])
 	if test "x$_ACJNI_JAVAC" = xno; then
-		AC_MSG_ERROR([cannot find JDK; try setting \$JAVAC or \$JAVA_HOME])
+		AC_MSG_WARN([cannot find JDK; try setting \$JAVAC or \$JAVA_HOME])
 	fi
 	_ACJNI_FOLLOW_SYMLINKS("$_ACJNI_JAVAC")
 	_JTOPDIR=`echo "$_ACJNI_FOLLOWED" | sed -e 's://*:/:g' -e 's:/[[^/]]*$::'`
@@ -76,17 +76,29 @@ _AS_ECHO_LOG([_JINC=$_JINC])
 # On Mac OS X 10.6.4, jni.h is a symlink:
 # /System/Library/Frameworks/JavaVM.framework/Versions/Current/Headers/jni.h
 # -> ../../CurrentJDK/Headers/jni.h.
-AC_CHECK_FILE([$_JINC/jni.h],
-	[JNI_INCLUDE_DIRS="$JNI_INCLUDE_DIRS $_JINC"],
-	[_JTOPDIR=`echo "$_JTOPDIR" | sed -e 's:/[[^/]]*$::'`
-	 AC_CHECK_FILE([$_JTOPDIR/include/jni.h],
-		[JNI_INCLUDE_DIRS="$JNI_INCLUDE_DIRS $_JTOPDIR/include"],
-                AC_MSG_ERROR([cannot find JDK header files]))
-	])
+
+AC_CACHE_CHECK(jni headers, ac_cv_jni_header_path,
+[
+if test -f "$_JINC/jni.h"; then
+  ac_cv_jni_header_path="$_JINC"
+  JNI_INCLUDE_DIRS="$JNI_INCLUDE_DIRS $ac_cv_jni_header_path"
+else
+  _JTOPDIR=`echo "$_JTOPDIR" | sed -e 's:/[[^/]]*$::'`
+  if test -f "$_JTOPDIR/include/jni.h"; then
+    ac_cv_jni_header_path="$_JTOPDIR/include"
+    JNI_INCLUDE_DIRS="$JNI_INCLUDE_DIRS $ac_cv_jni_header_path"
+  else
+    ac_cv_jni_header_path=none
+  fi
+fi
+])
+
+
 
 # get the likely subdirectories for system specific java includes
 case "$host_os" in
 bsdi*)          _JNI_INC_SUBDIRS="bsdos";;
+darwin*)        _JNI_INC_SUBDIRS="darwin";;
 freebsd*)       _JNI_INC_SUBDIRS="freebsd";;
 linux*)         _JNI_INC_SUBDIRS="linux genunix";;
 osf*)           _JNI_INC_SUBDIRS="alpha";;
@@ -96,13 +108,15 @@ cygwin*)	_JNI_INC_SUBDIRS="win32";;
 *)              _JNI_INC_SUBDIRS="genunix";;
 esac
 
-# add any subdirectories that are present
-for JINCSUBDIR in $_JNI_INC_SUBDIRS
-do
-    if test -d "$_JTOPDIR/include/$JINCSUBDIR"; then
-         JNI_INCLUDE_DIRS="$JNI_INCLUDE_DIRS $_JTOPDIR/include/$JINCSUBDIR"
-    fi
-done
+if test "x$ac_cv_jni_header_path" != "xnone"; then
+  # add any subdirectories that are present
+  for JINCSUBDIR in $_JNI_INC_SUBDIRS
+  do
+      if test -d "$_JTOPDIR/include/$JINCSUBDIR"; then
+           JNI_INCLUDE_DIRS="$JNI_INCLUDE_DIRS $_JTOPDIR/include/$JINCSUBDIR"
+      fi
+  done
+fi
 ])
 
 # _ACJNI_FOLLOW_SYMLINKS <path>