Add bootstrap-cet.mk to bootstrap GCC with Intel CET

Bootstrap GCC with Intel CET by configuring GCC with

--with-build-config="bootstrap-cet bootstrap-debug"

Tested on Linux/i686 and Linux/x86-64.

config/

	* bootstrap-cet.mk: New file.

gcc/

	* doc/install.texi: Document bootstrap-cet.

From-SVN: r254043

config/ChangeLog

+2017-10-24  H.J. Lu  <hongjiu.lu@intel.com>
+
+	* bootstrap-cet.mk: New file.
+
 2017-06-19  Martin Liska  <mliska@suse.cz>
 
 	* bootstrap-lto-noplugin.mk: Enable -flto in all PGO stages.

config/bootstrap-cet.mk

+# This option enables -fcf-protection -mcet for stage2 and stage3.
+
+STAGE2_CFLAGS += -fcf-protection -mcet
+STAGE3_CFLAGS += -fcf-protection -mcet

gcc/ChangeLog

 2017-10-24  H.J. Lu  <hongjiu.lu@intel.com>
 
+	* doc/install.texi: Document bootstrap-cet.
+
+2017-10-24  H.J. Lu  <hongjiu.lu@intel.com>
+
 	PR target/82659
 	* config/i386/i386.c (rest_of_insert_endbranch): Don't insert
 	ENDBR instruction at function entrance if function is only

gcc/doc/install.texi

@@ -2492,6 +2492,13 @@ useful to verify the full @option{-fcompare-debug} testing coverage.  It
 must be used along with @code{bootstrap-debug-lean} and
 @code{bootstrap-debug-lib}.
 
+@item @samp{bootstrap-cet}
+This option enables Intel CET for host tools during bootstrapping.
+@samp{BUILD_CONFIG=bootstrap-cet} is equivalent to adding
+@option{-fcf-protection -mcet} to @samp{BOOT_CFLAGS}.  This option
+assumes that the host supports Intel CET (e.g. GNU assembler version
+2.30 or later).
+
 @item @samp{bootstrap-time}
 Arranges for the run time of each program started by the GCC driver,
 built in any stage, to be logged to @file{time.log}, in the top level of