In target-support.exp mark that ARC uClibc toolchain doesn't support position independent executables. This caused hunderds of failed tests.

2013-06-12  Anton Kolesov <anton.kolesov@synopsys.com>

    * testsuite/lib/target-supports.exp: Disable position independent
    executable (-fpie, -fPIE) tests for arc*-*-linux* because they are not
    supported.