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


git-svn-id: a21e2c1a9f1a66aa2b49a2fb7314df0f83771e9b@1373 0101bb08-14d6-0310-b084-bc0e0c8e3800

peterdocter/ogg,svn2github/libogg,soundcloud/ogg,fcoulombe/ogg,peterdocter/ogg,svn2github/libogg,soundcloud/ogg,svn2github/ogg,fcoulombe/ogg,svn2github/ogg