This patch adds support for the ARMv8-M Security Extensions
'cmse_nonsecure_entry' attribute. In this patch we implement the
attribute handling and diagnosis around the attribute. See Section 5.4
of ARM®v8-M Security Extensions
(http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/index.html).

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

        * config/arm/arm.c (arm_handle_cmse_nonsecure_entry): New.
        (arm_attribute_table): Added cmse_nonsecure_entry
        (arm_compute_func_type): Handle cmse_nonsecure_entry.
        (cmse_func_args_or_return_in_stack): New.
        (arm_handle_cmse_nonsecure_entry): New.
        * config/arm/arm.h (ARM_FT_CMSE_ENTRY): New macro define.
        (IS_CMSE_ENTRY): Likewise.

*** 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: New.