[PATCH] MIPS: Fix the GCC version check for `__multi3' workaround

[Maciej W. Rozycki]

It was only GCC 10 that fixed a MIPS64r6 code generation issue with a 
`__multi3' libcall inefficiently produced to perform 64-bit widening 
multiplication while suitable machine instructions exist to do such a 
calculation.  The fix went in with GCC commit 48b2123f6336 ("re PR 
target/82981 (unnecessary __multi3 call for mips64r6 linux kernel)").

Adjust our code accordingly, removing build failures such as:

mips64-linux-ld: lib/math/div64.o: in function `mul_u64_add_u64_div_u64':
div64.c:(.text+0x84): undefined reference to `__multi3'

with the GCC versions affected.

Fixes: ebabcf17bcd7 ("MIPS: Implement __multi3 for GCC7 MIPS64r6 builds")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202601140146.hMLODc6v-lkp@xxxxxxxxx/
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v4.15+
---
 arch/mips/lib/multi3.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

linux-mips-multi3-gcc10.diff
Index: linux-macro/arch/mips/lib/multi3.c
===================================================================
--- linux-macro.orig/arch/mips/lib/multi3.c
+++ linux-macro/arch/mips/lib/multi3.c
@@ -4,12 +4,12 @@
 #include "libgcc.h"
 
 /*
- * GCC 7 & older can suboptimally generate __multi3 calls for mips64r6, so for
+ * GCC 9 & older can suboptimally generate __multi3 calls for mips64r6, so for
  * that specific case only we implement that intrinsic here.
  *
  * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
  */
-#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 8)
+#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 10)
 
 /* multiply 64-bit values, low 64-bits returned */
 static inline long long notrace dmulu(long long a, long long b)
@@ -51,4 +51,4 @@ ti_type notrace __multi3(ti_type a, ti_t
 }
 EXPORT_SYMBOL(__multi3);
 
-#endif /* 64BIT && CPU_MIPSR6 && GCC7 */
+#endif /* 64BIT && CPU_MIPSR6 && GCC9 */