x86: Default CET run-time support to auto

CET has been added since GCC 8.  This patch defaults CET run-time support
to auto.  It enables CET run-time support if asssembler supports CET
instructions and multi-byte NOPs are enabled via SSE2.

config/

	* cet.m4 (GCC_CET_FLAGS): Change default to auto.

gcc/

	* configure: Regenerated.

libatomic/

	* configure: Regenerated.

libbacktrace/

	* configure: Regenerated.

libcc1/

	* configure: Regenerated.

libcpp/

	* configure: Regenerated.

libdecnumber/

	* configure: Regenerated.

libgcc/

	* configure: Regenerated.

libgfortran/

	* configure: Regenerated.

libgomp/

	* configure: Regenerated.

libitm/

	* configure: Regenerated.

libobjc/

	* configure: Regenerated.

libquadmath/

	* configure: Regenerated.

libsanitizer/

	* configure: Regenerated.

libssp/

	* configure: Regenerated.

libstdc++-v3/

	* configure: Regenerated.

libvtv/

	* configure: Regenerated.

zlib/

	* configure: Regenerated.

libcpp/ChangeLog

@@ -1,3 +1,7 @@
+2020-05-14  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* configure: Regenerated.
+
 2020-05-13  Jason Merrill  <jason@redhat.com>
 
 	* include/cpplib.h (enum c_lang): Change CXX2A to CXX20.

libcpp/configure

@@ -7525,10 +7525,35 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
     ;;
 esac
 
+save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -fcf-protection=none"
+save_LDFLAGS="$LDFLAGS"
+LDFLAGS="$LDFLAGS -Wl,-z,ibt,-z,shstk"
 if test x$may_have_cet = xyes; then
-  save_LDFLAGS="$LDFLAGS"
-  LDFLAGS="$LDFLAGS -Wl,-z,ibt,-z,shstk"
-  if test "$cross_compiling" = yes; then :
+  # Check whether -fcf-protection=none -Wl,-z,ibt,-z,shstk work.
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+return 0;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  may_have_cet=yes
+else
+  may_have_cet=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+if test x$may_have_cet = xyes; then
+  if test x$cross_compiling = xno; then
+    if test "$cross_compiling" = yes; then :
   { { $as_echo "$as_me:${as_lineno-$LINENO}: error: in \`$ac_pwd':" >&5
 $as_echo "$as_me: error: in \`$ac_pwd':" >&2;}
 as_fn_error $? "cannot run test program while cross compiling
@@ -7573,10 +7598,14 @@ rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
   conftest.$ac_objext conftest.beam conftest.$ac_ext
 fi
 
-  LDFLAGS="$save_LDFLAGS"
-  if test x$enable_cet = xno -a x$have_cet = xyes; then
-    as_fn_error $? "Intel CET must be enabled on Intel CET enabled host" "$LINENO" 5
+    if test x$enable_cet = xno -a x$have_cet = xyes; then
+      as_fn_error $? "Intel CET must be enabled on Intel CET enabled host" "$LINENO" 5
+    fi
   fi
+else
+  # Enable CET in cross compiler if possible so that it will run on both
+  # CET and non-CET hosts.
+  have_cet=yes
 fi
 if test x$enable_cet = xyes; then
   CET_HOST_FLAGS="-fcf-protection"
@@ -7586,6 +7615,8 @@ else
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
 $as_echo "no" >&6; }
 fi
+CFLAGS="$save_CFLAGS"
+LDFLAGS="$save_LDFLAGS"
 
 case x$enable_languages in
 *jit*)