Also set CT_DEBUGROOT_DIR for non sysroot-ed toolchains.

In the non-sysroot-ed case, the debuf-root directory would not be set;
debug tools would have been installed God-only-knows-where...

Spotted by Bart van der Meulen <bartvdrmeulen@gmail.com>.
(transplanted from 634ffd14d936154464fd714ed29ed44c8e16ae02)

scripts/crosstool-NG.sh.in

@@ -255,6 +255,7 @@ if [ -z "${CT_RESTART}" ]; then
     else
         # plain old way. All libraries in prefix/target/lib
         CT_SYSROOT_DIR="${CT_PREFIX_DIR}/${CT_TARGET}"
+        CT_DEBUGROOT_DIR="${CT_SYSROOT_DIR}"
         CT_HEADERS_DIR="${CT_SYSROOT_DIR}/include"
         # hack!  Always use --with-sysroot for binutils.
         # binutils 2.14 and later obey it, older binutils ignore it.