This patch adds support ARMv8-M's Security Extension's
cmse_nonsecure_caller intrinsic. This intrinsic is used to check whether
an entry function was called from a non-secure state.
See Section 5.4.3 of ARM®v8-M Security Extensions: Requirements on
Development Tools
(http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/index.html)
for further details.

The FIXME in config/arm/arm_cmse.h is for a diagnostic message that is
suggested in the ARMv8-M Security Extensions document mentioned above,
to diagnose the use of the cmse_nonsecure_caller intrinsic outside of
functions with the 'cmse_nonsecure_entry' attribute.  Checking whether
the intrinsic is called from within such functions can easily be done
inside 'arm_expand_builtin'. However, making the warning point to the
right location is more complicated.  The ARMv8-M Security Extensions
specification does mention that such a diagnostic might become
mandatory, so I might have to pick this up later, otherwise it is left
as a potential extra feature.


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

        * config/arm/arm-builtins.c (arm_builtins): Define
        ARM_BUILTIN_CMSE_NONSECURE_CALLER.
        (bdesc_2arg): Add line for cmse_nonsecure_caller.
        (arm_expand_builtin): Handle cmse_nonsecure_caller.
        * config/arm/arm_cmse.h (cmse_nonsecure_caller): New.

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

        * gcc.target/arm/cmse/cmse-1.c: Add test for
        cmse_nonsecure_caller.