MIPS: UAPI: Ignore __arch_swab{16,32,64} when using MIPS16

Some GCC versions (e.g. 4.8.3) can incorrectly inline a function with
MIPS32 instructions into another function with MIPS16 code [1], causing
the assembler to genereate incorrect binary code or fail right away
complaining about unrecognized opcode.

In the case of __arch_swab{16,32}, when inlined by the compiler with
flags `-mips32r2 -mips16 -Os', the assembler can fail with the following
error.

    {standard input}:79: Error: unrecognized opcode `wsbh $2,$2'

For performance concerns and to workaround the issue already existing in
older compilers, just ignore these 2 functions when compiling with
mips16 enabled.

 [1] Inlining nomips16 function into mips16 function can result in
     undefined builtins, https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55777

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11241/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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

@@ -13,8 +13,9 @@
 
 #define __SWAB_64_THRU_32__
 
-#if (defined(__mips_isa_rev) && (__mips_isa_rev >= 2)) ||		\
-    defined(_MIPS_ARCH_LOONGSON3A)
+#if !defined(__mips16) &&					\
+	((defined(__mips_isa_rev) && (__mips_isa_rev >= 2)) ||	\
+	 defined(_MIPS_ARCH_LOONGSON3A))
 
 static inline __attribute_const__ __u16 __arch_swab16(__u16 x)
 {
@@ -65,5 +66,5 @@ static inline __attribute_const__ __u64 __arch_swab64(__u64 x)
 }
 #define __arch_swab64 __arch_swab64
 #endif /* __mips64 */
-#endif /* MIPS R2 or newer or Loongson 3A */
+#endif /* (not __mips16) and (MIPS R2 or newer or Loongson 3A) */
 #endif /* _ASM_SWAB_H */