relibc: add sys/ioccom.h with Linux IOC bitfield constants

Mesa 26.1.4's DRM UAPI headers include <sys/ioccom.h> as the BSD
include path for ioctl command encoding. The basic _IO / _IOR / _IOW /
_IOWR macros are already in <sys/ioctl.h> (musl-style via cbindgen),
but sys/ioccom.h adds the bitfield widths / masks / shifts / decoders
and the IOC_IN / IOC_OUT / IOC_INOUT / IOCSIZE_* macros that DRM and
other Linux UAPI consumers require.

This header includes <sys/ioctl.h> for the base macros and adds the
Linux-style constants as a thin shim. All new symbols are guarded
with #ifndef so including both headers is safe and idempotent.

This makes the Mesa-side 04-sys-ioccom-stub-header.patch redundant;
that patch can be removed from local/patches/mesa/ and the Mesa
recipe's patches list.

include/sys/ioccom.h

@@ -0,0 +1,97 @@
+#ifndef _SYS_IOCCOM_H
+#define _SYS_IOCCOM_H
+
+// Linux-compatible ioctl command encoding constants — supplements the
+// base _IOC / _IO / _IOR / _IOW / _IOWR macros from <sys/ioctl.h> with
+// the bitfield widths, masks, shifts, decoders, and IOC direction
+// macros that Linux UAPI headers (DRM, V4L2, etc.) expect.
+//
+// DRM headers include <sys/ioccom.h> as the BSD-naming path for ioctl
+// command encoding; relibc's <sys/ioctl.h> provides the basic macros
+// but not these constants. This header unifies them so DRM and other
+// Linux UAPI consumers build without a Mesa-side stub.
+
+#include <sys/ioctl.h>
+
+#ifndef _IOC_NRBITS
+#define _IOC_NRBITS    8
+#endif
+#ifndef _IOC_TYPEBITS
+#define _IOC_TYPEBITS  8
+#endif
+#ifndef _IOC_SIZEBITS
+#define _IOC_SIZEBITS  14
+#endif
+#ifndef _IOC_DIRBITS
+#define _IOC_DIRBITS   2
+#endif
+
+#ifndef _IOC_NRMASK
+#define _IOC_NRMASK    ((1 << _IOC_NRBITS) - 1)
+#endif
+#ifndef _IOC_TYPEMASK
+#define _IOC_TYPEMASK  ((1 << _IOC_TYPEBITS) - 1)
+#endif
+#ifndef _IOC_SIZEMASK
+#define _IOC_SIZEMASK  ((1 << _IOC_SIZEBITS) - 1)
+#endif
+#ifndef _IOC_DIRMASK
+#define _IOC_DIRMASK   ((1 << _IOC_DIRBITS) - 1)
+#endif
+
+#ifndef _IOC_NRSHIFT
+#define _IOC_NRSHIFT    0
+#endif
+#ifndef _IOC_TYPESHIFT
+#define _IOC_TYPESHIFT  (_IOC_NRSHIFT + _IOC_NRBITS)
+#endif
+#ifndef _IOC_SIZESHIFT
+#define _IOC_SIZESHIFT  (_IOC_TYPESHIFT + _IOC_TYPEBITS)
+#endif
+#ifndef _IOC_DIRSHIFT
+#define _IOC_DIRSHIFT   (_IOC_SIZESHIFT + _IOC_SIZEBITS)
+#endif
+
+// _IOC_TYPECHECK wraps the ioctl size argument in a sizeof() for type
+// safety. The musl/relibc _IOW / _IOR / _IOWR macros already call
+// sizeof internally on the third argument; this macro is provided for
+// callers that compose ioctl numbers directly (e.g. DRM).
+#ifndef _IOC_TYPECHECK
+#define _IOC_TYPECHECK(t) (sizeof(t))
+#endif
+
+// _IOC_DIR / _IOC_TYPE / _IOC_NR / _IOC_SIZE decode the fields of an
+// ioctl number. Linux UAPI callers use these to inspect ioctls.
+#ifndef _IOC_DIR
+#define _IOC_DIR(nr)  (((nr) >> _IOC_DIRSHIFT)  & _IOC_DIRMASK)
+#endif
+#ifndef _IOC_TYPE
+#define _IOC_TYPE(nr) (((nr) >> _IOC_TYPESHIFT) & _IOC_TYPEMASK)
+#endif
+#ifndef _IOC_NR
+#define _IOC_NR(nr)   (((nr) >> _IOC_NRSHIFT)   & _IOC_NRMASK)
+#endif
+#ifndef _IOC_SIZE
+#define _IOC_SIZE(nr) (((nr) >> _IOC_SIZESHIFT) & _IOC_SIZEMASK)
+#endif
+
+// IOC_IN / IOC_OUT / IOC_INOUT are the values stored in the direction
+// field of an ioctl number when constructing one without _IO / _IOR /
+// _IOW / _IOWR.
+#ifndef IOC_IN
+#define IOC_IN     (_IOC_WRITE  << _IOC_DIRSHIFT)
+#endif
+#ifndef IOC_OUT
+#define IOC_OUT    (_IOC_READ   << _IOC_DIRSHIFT)
+#endif
+#ifndef IOC_INOUT
+#define IOC_INOUT  ((_IOC_WRITE | _IOC_READ) << _IOC_DIRSHIFT)
+#endif
+#ifndef IOCSIZE_MASK
+#define IOCSIZE_MASK  (_IOC_SIZEMASK << _IOC_SIZESHIFT)
+#endif
+#ifndef IOCSIZE_SHIFT
+#define IOCSIZE_SHIFT (_IOC_SIZESHIFT)
+#endif
+
+#endif /* _SYS_IOCCOM_H */