The GPU has much tighter requirements for handling IO functions.
Previously we attempted to define the GPU as one of the platform files.
Using a common interface allowed us to easily define these functions
without much extra work. However, it became more clear that this was a
poor fit for the GPU. The file interface uses function pointers, which
prevented inlining and caused bad perfromance and resource usage on the
GPU. Further, using an actual `FILE` type rather than referring to it as
a host stub prevented us from usin files coming from the host on the GPU
device.
After talking with @sivachandra, the approach now is to simply define
GPU specific versions of the functions we intend to support. Also, we
are ignoring `errno` for the time being as it is unlikely we will ever
care about supporting it fully.
Reviewed By: sivachandra
Differential Revision: https://reviews.llvm.org/D157427
d04494ccc9