Allow the user to specify their own CFLAGS and LDFLAGS when they run configure/autogen.sh.
Allow the user to specify their own CFLAGS and LDFLAGS when they run
configure/autogen.sh.

If the environment variables CFLAGS and/or LDFLAGS are set, their values
are saved and appended to the values that are set in configure.in.

Example (csh-style, cope):

% setenv CFLAGS -DVORBIS_ROCKS=1
% ./autogen.sh

svn path=/trunk/ogg/; revision=1373

felipebetancur/ogg,nicolaichuk/ogg,mwgoldsmith/ogg,ShiftMediaProject/ogg,xiph/ogg,emscripten-ports/Ogg,youfearm3/ogg,youfearm3/ogg,ksophocleous/ogg,mwgoldsmith/ogg,eidy/libogg,nicolaichuk/ogg,brion/ogg,emscripten-ports/Ogg,ksophocleous/ogg,eidy/libogg,ShiftMediaProject/ogg,felipebetancur/ogg,brion/ogg,xiph/ogg