as i saw several warnings at gst-ffmpeg autogen, i did the following grep :
grep -r "head -[0-9]" /usr/portage/distfiles/cvs-src/gst*

and found :

gst-ffmpeg/gst-libs/ext/ffmpeg/patch/autotools.diff:+       
actual_version=`$checkprog --version | head -1 | \

and

gst-editor/common/m4/ax_create_stdint_h.m4:ac_cv_stdint_message="using gnu
compiler "`$CC --version | head -1`
/gst-ffmpeg/common/m4/ax_create_stdint_h.m4:ac_cv_stdint_message="using gnu
compiler "`$CC --version | head -1`
gst-player/common/m4/ax_create_stdint_h.m4:ac_cv_stdint_message="using gnu
compiler "`$CC --version | head -1`
gst-plugins/common/m4/ax_create_stdint_h.m4:ac_cv_stdint_message="using gnu
compiler "`$CC --version | head -1`
gstreamer/common/m4/ax_create_stdint_h.m4:ac_cv_stdint_message="using gnu
compiler "`$CC --version | head -1`

head -number (or any number) as well as tail -number is deprecated and
non-portable. (and would be removed in later head/tail versions)

the following should be used : head -n number or tail -n number

as there is a 'common' CVS repository, i suppose it contains this directory
for every gstreamer part, so only one change required.

the only part which a second bad use of head -1 is gst-ffmpeg


here are the warnings i have :

configure: slurping FFmpeg CVS source
configure: checking out ffmpeg cvs code from 2004-02-29 20:00 GMT into
gst-libs/ext/ffmpeg
cvs checkout: warning: failed to open
/usr/portage/tmp/portage/homedir/.cvspass for reading: No such file or
directory
configure: setting up ffmpeg build system and applying patches
checking for libtool >= 1.5...
  testing libtoolize... head: `-1' option is obsolete; use `-n 1' since
this will be removed in the future
found.
checking for autoconf >= 2.53...
  testing autoconf... head: `-1' option is obsolete; use `-n 1' since this
will be removed in the future
found.
checking for automake >= 1.6...
  testing automake... head: `-1' option is obsolete; use `-n 1' since this
will be removed in the future
too old (found version 1.5)
  testing automake-1.7... head: `-1' option is obsolete; use `-n 1' since
this will be removed in the future
found.
aclocal: configure.ac: 547: macro `AM_PATH_IMLIB' not found in library
checking whether byte ordering is bigendian... no