g++wrap: make it work with --enable-glibcxx-debug

* doc/org/g++wrap.in: Honor CPPFLAGS.

doc/org/g++wrap.in

@@ -5,7 +5,7 @@
 # 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 \
+@top_builddir@/libtool link @CXX@ @CXXFLAGS@ @CPPFLAGS@ -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@/buddy/src/libbddx.la 2> errors.$$