This cc1 option -fallow-half-arguments-and-returns allows __fp16 to be
passed by argument and returned, without giving an error. It is
currently always enabled for Arm and AArch64, by forcing the option in
the driver. This means any cc1 tests (especially those needing
arm_neon.h) need to specify the option too, to prevent the error from
being emitted.
This changes it to a target option instead, set to true for Arm and
AArch64. This allows the option to be removed. Previously it was implied
by -fnative_half_arguments_and_returns, which is set for certain
languages like open_cl, renderscript and hlsl, so that option now too
controls the errors. There were are few other non-arm uses of
-fallow-half-arguments-and-returns but I believe they were unnecessary.
The strictfp_builtins.c tests were converted from __fp16 to _Float16 to
avoid the issues.
Differential Revision: https://reviews.llvm.org/D133885
