use c++ for some more sources

Do a (superficial) port to c++ of some of the c sources. Update
deps. Fix a few compiler warnings.

guile/Makefile.am

@@ -35,6 +35,13 @@ AM_CFLAGS=						\
 	-Wno-missing-prototypes				\
 	-Wno-missing-declarations
 
+AM_CXXFLAGS=						\
+	$(ASAN_CFLAGS)					\
+	${WARN_CXXFLAGS}				\
+	-Wno-redundant-decls				\
+	-Wno-missing-declarations			\
+	-Wno-suggest-attribute=noreturn
+
 lib_LTLIBRARIES=					\
 	libguile-mu.la
 
@@ -45,6 +52,7 @@ libguile_mu_la_SOURCES=					\
 	mu-guile-message.hh
 
 libguile_mu_la_CFLAGS=$(AM_CFLAGS)
+libguile_mu_la_CXXFLAGS=$(AM_CXXFLAGS)
 
 libguile_mu_la_LIBADD=					\
 	${top_builddir}/lib/libmu.la			\
@@ -67,12 +75,14 @@ mu_guile_TEXINFOS=					\
 
 BUILT_SOURCES=$(XFILES)
 
-snarfcppopts= $(DEFS) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS)
+snarfcopts= $(DEFS) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS)
+snarfcxxopts= $(DEFS) $(AM_CPPFLAGS) $(CPPFLAGS) $(AM_CXXFLAGS) $(CXXFLAGS)
+
 SUFFIXES = .x .doc
 .c.x:
-	$(AM_V_GEN) $(GUILE_SNARF) -o $@ $< $(snarfcppopts)
+	$(AM_V_GEN) $(GUILE_SNARF) -o $@ $< $(snarfcopts)
 .cc.x:
-	$(AM_V_GEN) $(GUILE_SNARF) -o $@ $< $(snarfcppopts)
+	$(AM_V_GEN) $(GUILE_SNARF) -o $@ $< $(snarfcxxopts)
 
 
 # FIXME: GUILE_SITEDIR would be better, but that