gcc-target 5.1: fix for libcc1

gcc-target 5.1: fix for libcc1

Fixed:
* gcc 5 introduces a plugin libcc1.so, which is used by gdb, the target
gcc didn't build it in the past because gcc_cv_objdump is null, and
the error was:
gcc-5.2.0/libcc1/configure: line 14531: -T: command not found

This only happens for tar gcc as the code shows:
  if test x$build = x$host; then
    export_sym_check="objdump${exeext} -T"
  elif test x$host = x$target; then
    export_sym_check="$gcc_cv_objdump -T"
  else
    export_sym_check=
  fi

* Install libcc1.so and libcc1plugin.so to
  $(libexecdir)/gcc/$(target_noncanonical)/$(gcc_version) as lto-plugin did.

* Use sed command to fix bad RPATH iussue.

[YOCTO #7956]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>