Support _IONBF buffering for read_unlocked. Add the functions
read_unlocked_nbf() and read_unlocked_fbf().

Fixes: #120155

This patch enables most of the libc entrypoints for riscv, except for fstatvfs, statvfs, dmull and fmull which are currently failing compilation. float16 is also not added, as rv32 doesn't seem to support it yet.

This patch also fixes the call to seek, which should take an off_t, and was missed in PR #68269.

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

reland of https://github.com/llvm/llvm-project/pull/98215

Additionally adds proxy headers for FILE and the fopencookie types

The arm32 build has been failing due to redefinitions of the off_t type.
This patch fixes this by moving off_t to a proper proxy header. To do
this, it also moves stdio macros to a proxy header to hopefully avoid
including this proxy header alongside this public stdio.h.

Reverts llvm/llvm-project#98215

Breaks linux bots

The arm32 build has been failing due to redefinitions of the off_t type.
This patch fixes this by moving off_t to a proper proxy header. To do
this, it also moves stdio macros to a proxy header to hopefully avoid
including this proxy header alongside this public stdio.h.

Summary:
Including stdio here caused some multiple definitions on overlay mode.
Just include `off_t` directly.

Is this correct for 32-bit targets? Will investigate further after
fixing bots.

Summary:
The `stdio.h` header should define `off_t` as defined for the platform.
This will use the system's in overlay mode, or what the llvm-libc-types
deems correct. If this `off_t` is incorrect it should be changed in
`llvm-libc-types`. This fixes the GPU build.