[ARM] Rename FPSCR builtins to correct names

[ARM] Rename FPSCR builtins to correct names

The GCC documentation in section 6.60.8 ARM Floating Point Status and
Control Intrinsics states that the FPSCR register can be read and
written to using the intrinsics __builtin_arm_get_fpscr and
__builtin_arm_set_fpscr. However, these are misnamed within GCC itself
and these intrinsic names are not recognised.

This patch corrects the intrinsic names to match the documentation, and
adds tests to verify these intrinsics generate the correct
instructions.

2017-05-04  Prakhar Bahuguna  <prakhar.bahuguna@arm.com>

    gcc/
    * gcc/config/arm/arm-builtins.c (arm_init_builtins): Rename
    __builtin_arm_ldfscr to __builtin_arm_get_fpscr, and rename
    __builtin_arm_stfscr to __builtin_arm_set_fpscr.

    gcc/testsuite/
    * gcc.target/arm/fpscr.c: New file.

From-SVN: r247584