autoconf 2.52: FLAGS accumulation

[Christian Cornelssen]

Dear autoconf maintainers,

After `CFLAGS="..." CXXFLAGS="..." ./configure', every invocation of
`config.status --recheck' command adds one more CFLAGS and CXXFLAGS
definition to configure's command line.  Meanwhile, about six
identical definition clusters have accumulated, taking more than one
screen page for the command line.  I think that configure should try
to avoid such replication.

Nevertheless, autoconf is a great tool.

Sincerely,

Christian Cornelssen