gdbsupport: re-generate Makefile.in

It looks like after doing last minute changes to Makefile.am in commit
06b3c5b ("gdbsupport: rename source files to .cc"), I forgot to
re-generate Makefile.in.  This patch fixes it.

gdbsupport/ChangeLog:

	* Makefile.in: Re-generate.

gdbsupport/ChangeLog

@@ -1,3 +1,7 @@
+2020-03-03  Simon Marchi  <simon.marchi@efficios.com>
+
+	* Makefile.in: Re-generate.
+
 2020-02-28  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	* gdb-dlfcn.h (gdb_dlopen): Update comment.

gdbsupport/Makefile.in

@@ -354,7 +354,7 @@ AM_CPPFLAGS = -I$(srcdir)/../include -I$(srcdir)/../gdb \
     -I../gnulib/import -I$(srcdir)/../gnulib/import \
     -I.. -I$(srcdir)/.. $(INCINTL) -I../bfd -I$(srcdir)/../bfd
 
-AM_CXXFLAGS = $(CXX_DIALECT) $(WARN_CFLAGS) $(WERROR_CFLAGS)
+AM_CXXFLAGS = $(WARN_CFLAGS) $(WERROR_CFLAGS)
 noinst_LIBRARIES = libgdbsupport.a
 @SELFTEST_TRUE@selftest = selftest.cc
 libgdbsupport_a_SOURCES = \
@@ -693,6 +693,8 @@ uninstall-am:
 .PRECIOUS: Makefile
 
 
+override CXX += $(CXX_DIALECT)
+
 # Double-check that no defines are missing from our configury.
 check-defines:
 	cd $(srcdir) && emacs --script check-defines.el