build: add missing leveldb defines

src/leveldb/build_detect_platform shows how upstream defines them.

These platform may not be able to fully build or run Bitcoin, but defining all
known to leveldb saves future hassle.

Now that all possible platforms are enumerated, specifying an unknown one is an
error.

configure.ac

@@ -541,10 +541,17 @@ case $host in
      CPPFLAGS="$CPPFLAGS -DMAC_OSX"
      OBJCXXFLAGS="$CXXFLAGS"
      ;;
+   *android*)
+     dnl make sure android stays above linux for hosts like *linux-android*
+     LEVELDB_TARGET_FLAGS="-DOS_ANDROID"
+     ;;
    *linux*)
      TARGET_OS=linux
      LEVELDB_TARGET_FLAGS="-DOS_LINUX"
      ;;
+   *kfreebsd*)
+     LEVELDB_TARGET_FLAGS="-DOS_KFREEBSD"
+     ;;
    *freebsd*)
      LEVELDB_TARGET_FLAGS="-DOS_FREEBSD"
      ;;
@@ -554,10 +561,17 @@ case $host in
    *netbsd*)
      LEVELDB_TARGET_FLAGS="-DOS_NETBSD"
      ;;
+   *dragonfly*)
+     LEVELDB_TARGET_FLAGS="-DOS_DRAGONFLYBSD"
+     ;;
+   *solaris*)
+     LEVELDB_TARGET_FLAGS="-DOS_SOLARIS"
+     ;;
+   *hpux*)
+     LEVELDB_TARGET_FLAGS="-DOS_HPUX"
+     ;;
    *)
-     OTHER_OS=`echo ${host_os} | awk '{print toupper($0)}'`
-     AC_MSG_WARN([Guessing LevelDB OS as OS_${OTHER_OS}, please check whether this is correct, if not add an entry to configure.ac.])
-     LEVELDB_TARGET_FLAGS="-DOS_${OTHER_OS}"
+     AC_MSG_ERROR(Cannot build leveldb for $host. Please file a bug report.)
      ;;
 esac