MIPS: Fix CONFIG_CPU_DADDI_WORKAROUNDS `modules_install' regression

Remove a build-time check for the presence of the GCC `-msym32' option.
This option has been there since GCC 4.1.0, which is below the minimum
required as at commit 805b2e1d ("kbuild: include Makefile.compiler
only when compiler is needed"), when an error message:

arch/mips/Makefile:306: *** CONFIG_CPU_DADDI_WORKAROUNDS unsupported without -msym32.  Stop.

started to trigger for the `modules_install' target with configurations
such as `decstation_64_defconfig' that set CONFIG_CPU_DADDI_WORKAROUNDS,
because said commit has made `cc-option-yn' an undefined function for
non-build targets.
Reported-by: Jan-Benedict Glaw <jbglaw@lug-owl.de>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Fixes: 805b2e1d ("kbuild: include Makefile.compiler only when compiler is needed")
Cc: stable@vger.kernel.org # v5.13+
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/Makefile

@@ -299,8 +299,8 @@ ifdef CONFIG_64BIT
     endif
   endif
 
-  ifeq ($(KBUILD_SYM32)$(call cc-option-yn,-msym32), yy)
-    cflags-y += -msym32 -DKBUILD_64BIT_SYM32
+  ifeq ($(KBUILD_SYM32), y)
+    cflags-$(KBUILD_SYM32) += -msym32 -DKBUILD_64BIT_SYM32
   else
     ifeq ($(CONFIG_CPU_DADDI_WORKAROUNDS), y)
       $(error CONFIG_CPU_DADDI_WORKAROUNDS unsupported without -msym32)