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/vorbis/; revision=1373

erikd/vorbis,felipebetancur/vorbis,eidy/vorbis,felipebetancur/vorbis,youfearm3/vorbis,nicolaichuk/vorbis,nicolaichuk/vorbis,emscripten-ports/Vorbis,felipebetancur/vorbis,ksophocleous/vorbis,mwgoldsmith/vorbis,ShiftMediaProject/vorbis,emscripten-ports/Vorbis,ksophocleous/vorbis,ShiftMediaProject/vorbis,mwgoldsmith/vorbis,mwgoldsmith/vorbis,youfearm3/vorbis,nicolaichuk/vorbis,felipebetancur/vorbis,ksophocleous/vorbis,ShiftMediaProject/vorbis,emscripten-ports/Vorbis,nicolaichuk/vorbis,youfearm3/vorbis,ShiftMediaProject/vorbis,ShiftMediaProject/vorbis,youfearm3/vorbis,ShiftMediaProject/vorbis,eidy/vorbis,mwgoldsmith/vorbis,erikd/vorbis,erikd/vorbis,eidy/vorbis,emscripten-ports/Vorbis,ksophocleous/vorbis,eidy/vorbis,erikd/vorbis