org: detect C++ errors

* doc/org/g++wrap.in: Save error messages.
* doc/Makefile.am: Display them at the end of the compilation.

doc/Makefile.am

@@ -57,9 +57,12 @@ dist_pkgdata_DATA = $(srcdir)/spot.tag
 .PHONY: org org-man
 org:
 	cd $(top_builddir) && $(MAKE) doc/org/init.el
-	rm -rf $(srcdir)/userdoc
+	rm -rf $(srcdir)/userdoc $(builddir)/org/org.errors
 	$(MAKE) org-man org/plantuml.jar
 	$(EMACS) --batch -Q -l org/init.el
+	if test -s $(builddir)/org/org.errors; then \
+	  cat $(builddir)/org/org.errors; exit 1; \
+        else :; fi
 
 org/plantuml.jar:
 	wget http://downloads.sourceforge.net/project/plantuml/plantuml.jar -O org/plantuml.jar || curl http://downloads.sourceforge.net/project/plantuml/plantuml.jar -o org/plantuml.jar

doc/org/g++wrap.in

@@ -1,6 +1,17 @@
 #!/bin/sh
 # This is a wrapper around the compiler, to ensure that the code
 # example run from the org-mode file are all linked with Spot.
-exec @top_builddir@/libtool link @CXX@ -std=c++11 -Wall \
+#
+# Also we save errors to org.errors, so that we can detect issues
+# after org-mode has exported everything.  Otherwise these errors
+# would go undetected.
+@top_builddir@/libtool link @CXX@ @CXXFLAGS@ -Wall -Werror \
  -I@abs_top_builddir@ -I@abs_top_srcdir@ -I@abs_top_srcdir@/buddy/src \
-     "$@" @abs_top_builddir@/spot/libspot.la
+ "$@" @abs_top_builddir@/spot/libspot.la 2> errors.$$
+code=$?
+if test $code -ne 0 && test -s errors.$$; then
+    cat errors.$$ >>org.errors
+    cat errors.$$ >&2
+fi
+rm -f errors.$$
+exit $code