libc/uClibc: move content of do_libc_headers into do_libc_start_files

It is unnecessary to split C library preparation into two steps, as only
one really makes sense. So, do_libc_headers is bound to be withdrawn
short-term, in favor of do_libc_start_files.

uClibc already had all its start files installation in do_libc_headers, and
do_libc_start_files was empty, just migrate the content of the former into
the latter.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 http://sourceware.org/ml/binutils/2007-07/msg00401.html

 http://sourceware.org/bugzilla/show_bug.cgi?id=4970

 --- binutils/configure

 +++ binutils/configure

 @@ -5601,6 +5601,7 @@ case "${host}" in

    *-*-mingw* | *-*-cygwin ) RPATH_ENVVAR=PATH ;;

    *) RPATH_ENVVAR=LD_LIBRARY_PATH ;;

  esac

 +RPATH_ENVVAR="cant_touch_this_nah_nah_nah"

  # On systems where the dynamic library environment variable is PATH,

  if test "$RPATH_ENVVAR" = PATH; then