Mount the devpts file system.

The lack of a devpts file system was causing mysterious GNU Binutils
test suite failures, with these "spawn failed" errors in the test log:

    Test Run By root on Sun Dec  8 20:36:45 2013
    Native configuration is x86_64-unknown-linux-gnu

                    === binutils tests ===

    Schedule of variations:
        unix

    Running target unix
    Using /usr/share/dejagnu/baseboards/unix.exp as board description file for target.
    Using /usr/share/dejagnu/config/unix.exp as generic interface file for target.
    Using /usr/src/binutils_2.23.2-1/tmp/src/binutils/testsuite/config/default.exp as tool-and-target-specific interface file.
    Running /usr/src/binutils_2.23.2-1/tmp/src/binutils/testsuite/binutils-all/ar.exp ...
    /usr/src/binutils_2.23.2-1/tmp/build-core-linux-eglibc/binutils/ar rc tmpdir/artest.a tmpdir/abcdefghijklmnopqrstuvwxyz1 tmpdir/abcdefghijklmnopqrstuvwxyz2
    Executing on host: /usr/src/binutils_2.23.2-1/tmp/build-core-linux-eglibc/binutils/ar rc tmpdir/artest.a tmpdir/abcdefghijklmnopqrstuvwxyz1 tmpdir/abcdefghijklmnopqrstu
    vwxyz2   (timeout = 300)
    spawn /usr/src/binutils_2.23.2-1/tmp/build-core-linux-eglibc/binutils/ar rc tmpdir/artest.a tmpdir/abcdefghijklmnopqrstuvwxyz1 tmpdir/abcdefghijklmnopqrstuvwxyz2M
    spawn failed
    [...]

                    === binutils Summary ===

    # of unexpected failures        6
    # of unresolved testcases       48
    # of untested testcases         7
    # of unsupported tests          4
    runtest completed at Sun Dec  8 20:36:45 2013

After spelunking through Binutils and DejaGnu code (exploring the great
remote_exec and local_exec procedures of DejaGnu), I tried the
following, which resulted in much more helpful information:

    $ expect
    expect1.1> spawn echo hello
    spawn echo hello
    The system has no more ptys.  Ask your system administrator to create more.
        while executing
    "spawn echo hello"

1 files changed, 3 insertions, 0 deletions

diff --git a/bootstrap-stage2-install.sh b/bootstrap-stage2-install.sh
index 819996d..e288bf8 100755
--- a/bootstrap-stage2-install.sh
+++ b/bootstrap-stage2-install.sh
@@ -64,6 +64,7 @@ clean_root()
 
 	case "${ARCH}" in
 		*-linux-*)
+			sudo umount dev/pts || true
 			sudo umount proc || true
 			sudo umount sys || true
 			sudo umount dev || true
@@ -160,6 +161,8 @@ setup_root()
 			sudo mount -t proc proc proc
 			sudo mount -t sysfs sys sys
 			sudo mount -o bind /dev dev
+			sudo mount -t devpts -o noexec,nosuid,gid=5,mode=0620 \
+				devpts dev/pts
 			;;
 	esac