bug#4434: add -Wdeclaration-after-statement to CFLAGS if supported

[Dan Nicolaescu <dann@ics.uci.edu>]

Dan Nicolaescu <dann@ics.uci.edu> writes:

  > Recently we've had a few instances of declarations being added in the
  > middle of a block.
  > 
  > gcc has a flag to warn about this.
  > 
  > Here's a patch to add this flag to CFLAGS (it mirrors what we already do
  > for  -Wno-pointer-sign).
  > 
  > OK to check in?

Stefan, any reason not to check this in?

I just run into compilation errors when compiling the current CVS on an
old machine that uses gcc-2.96, 3-4 files need fixing.


  > Index: configure.in
  > ===================================================================
  > RCS file: /cvsroot/emacs/emacs/configure.in,v
  > retrieving revision 1.607
  > diff -u -3 -p -u -p -r1.607 configure.in
  > --- configure.in 23 Aug 2009 02:15:00 -0000     1.607
  > +++ configure.in 14 Sep 2009 18:46:36 -0000
  > @@ -757,6 +757,19 @@ CFLAGS="$SAVE_CFLAGS"
  >  unset has_option
  >  unset SAVE_CFLAGS
  >  
  > +### Use -Wdeclaration-after-statement if the compiler supports it
  > +AC_MSG_CHECKING([whether gcc understands
  > -Wdeclaration-after-statement])
  > +SAVE_CFLAGS="$CFLAGS"
  > +CFLAGS="$CFLAGS -Wdeclaration-after-statement"
  > +AC_TRY_COMPILE([], [], has_option=yes, has_option=no,)
  > +if test $has_option = yes; then
  > +   C_WARNINGS_SWITCH="-Wdeclaration-after-statement $C_WARNINGS_SWITCH"
  > +fi
  > +AC_MSG_RESULT($has_option)
  > +CFLAGS="$SAVE_CFLAGS"
  > +unset has_option
  > +unset SAVE_CFLAGS
  > +
  >  #### Some other nice autoconf tests.
  >  
  >  dnl checks for programs