Alternative creation of TMPDIR in Windows.

Users of portableGit in Windows do not have mktemp.
TMPDIR ended up empty and compiler.js was created at /.
Good thing is "rm -rf " trap failed with empty arguments
and it did not remove everything.

bin/amberc

@@ -216,7 +216,8 @@ done
 LIBS="$TOBASE $TOLOAD"
 
 # Get a unique tempdir and make it get auto removed on exit
-TMPDIR=`mktemp -d amberc.XXXXXX`
+TMPDIR=`mktemp -d amberc.XXXXXX 2>>/dev/null` ||\
+    TMPDIR=/tmp/amberc.$$.`date +%s` && mkdir -p $TMPDIR
 trap "rm -rf $TMPDIR" EXIT