MIPS: Probe toolchain support of -msym32

msym32 is not supported by LLVM toolchain.
Workaround by probe toolchain support of msym32 for KBUILD_SYM32
feature.

Link: ClangBuiltLinux#1544
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: FlyGoat

arch/mips/Makefile

@@ -299,7 +299,7 @@ drivers-$(CONFIG_PCI)		+= arch/mips/pci/
 ifdef CONFIG_64BIT
   ifndef KBUILD_SYM32
     ifeq ($(shell expr $(load-y) \< 0xffffffff80000000), 0)
-      KBUILD_SYM32 = y
+      KBUILD_SYM32 = $(call cc-option-yn, -msym32)
     endif
   endif