Tell libtool to link libtsk as a C++ library.

Index: tsk/Makefile.am
--- tsk/Makefile.am.orig
+++ tsk/Makefile.am
@@ -4,6 +4,9 @@ SUBDIRS = base img vs fs hashdb auto pool util
 # Merge the libraries into one
 lib_LTLIBRARIES = libtsk.la
 libtsk_la_SOURCES =
+# hack to force linkage with a c++ compiler
+# https://www.gnu.org/software/automake/manual/html_node/Libtool-Convenience-Libraries.html
+nodist_EXTRA_libtsk_la_SOURCES = dummy.cpp
 libtsk_la_LIBADD = base/libtskbase.la img/libtskimg.la \
     vs/libtskvs.la fs/libtskfs.la hashdb/libtskhashdb.la \
     auto/libtskauto.la pool/libtskpool.la util/libtskutil.la