MIPS: Remove superfluous check for __linux__

When building BPF code using "clang -target bpf -c", clang does not
define __linux__.

To build BPF IR decoders the include linux/lirc.h is needed which
includes linux/types.h. Currently this workaround is needed:

https://git.linuxtv.org/v4l-utils.git/commit/?id=dd3ff81f58c4e1e6f33765dc61ad33c48ae6bb07

This check might otherwise be useful to stop users from using a non-linux
compiler, but if you're doing that you are going to have a lot more
trouble anyway.

Signed-off-by: Sean Young <[e-mail]>
Signed-off-by: Paul Burton <[e-mail]>
Patchwork: https://patchwork.linux-mips.org/patch/21149/
Cc: Ralf Baechle <[e-mail]>
Cc: James Hogan <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]

arch/mips/include/uapi/asm/sgidefs.h

···
 #define __ASM_SGIDEFS_H
 
 /*
- * Using a Linux compiler for building Linux seems logic but not to
- * everybody.
- */
-#ifndef __linux__
-#error Use a Linux compiler or give up.
-#endif
-
-/*
  * Definitions for the ISA levels
  *
  * With the introduction of MIPS32 / MIPS64 instruction sets definitions