This patch adds support for the ARMv8-M Security Extensions
'cmse_nonsecure_call' attribute. This attribute may only be used for
function types and when used in combination with the '-mcmse'
compilation flag. See Section 5.5 of ARM®v8-M Security Extensions
(http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/index.html).

We currently do not support cmse_nonsecure_call functions that pass
arguments or return variables on the stack and we diagnose this.

*** gcc/ChangeLog ***
2016-07-25  Andre Vieira        <andre.simoesdiasvieira@arm.com>
            Thomas Preud'homme  <thomas.preudhomme@arm.com>

        * config/arm/arm.c (gimplify.h): New include.
        (arm_handle_cmse_nonsecure_call): New.
        (arm_attribute_table): Added cmse_nonsecure_call.

*** gcc/testsuite/ChangeLog ***
2016-07-25  Andre Vieira        <andre.simoesdiasvieira@arm.com>
            Thomas Preud'homme  <thomas.preudhomme@arm.com>

        * gcc.target/arm/cmse/cmse-3.c: Add tests.
        * gcc.target/arm/cmse/cmse-4.c: Add tests.