GLIBC support for Xtensa

Testsuite failures:

FAIL: conform/POSIX2008/fcntl.h/linknamespace

FAIL: conform/POSIX2008/mqueue.h/linknamespace

FAIL: conform/POSIX2008/sys/stat.h/conform

FAIL: conform/XOPEN2K8/fcntl.h/linknamespace

FAIL: conform/XOPEN2K8/mqueue.h/linknamespace

FAIL: conform/XOPEN2K8/sys/stat.h/conform

FAIL: conform/XOPEN2K/fcntl.h/linknamespace

FAIL: conform/XOPEN2K/mqueue.h/linknamespace

FAIL: debug/backtrace-tst

FAIL: dlfcn/default

FAIL: iconvdata/mtrace-tst-loading

FAIL: iconvdata/tst-loading

FAIL: io/bug-ftw2

FAIL: io/ftwtest

FAIL: io/test-stat2

FAIL: io/test-utime

FAIL: io/tst-fts

FAIL: localedata/mtrace-tst-leaks

FAIL: localedata/tst-leaks

FAIL: malloc/tst-dynarray-fail

FAIL: malloc/tst-dynarray-fail-mem

FAIL: malloc/tst-mallocstate

FAIL: misc/tst-clone3

bad test?: futex syscall should have 6 arguments

FAIL: nptl/tst-backtrace1

FAIL: nptl/tst-cancel21

works if run manually

FAIL: nptl/tst-cancel7

FAIL: nptl/tst-cancelx21

works if run manually

FAIL: nptl/tst-cancelx7

FAIL: nptl/tst-stack4

Timeout, too many threads

FAIL: posix/tst-getaddrinfo5

FAIL: stdio-common/bug22

bad test?: expected exit status should be 1

FAIL: stdlib/tst-strtod-round

FAIL: string/tst-cmp

FAIL: wcsmbs/tst-wcstod-round