examples: use architecture specific memset() on RISC-V

Build the architecture specific memset() if configured.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/examples/api/Makefile b/examples/api/Makefile
index ec1643e..13e859c 100644
--- a/examples/api/Makefile
+++ b/examples/api/Makefile
@@ -43,8 +43,8 @@
 EXT_COBJ-y += lib/charset.o
 EXT_COBJ-$(CONFIG_LIB_UUID) += lib/uuid.o
 EXT_SOBJ-$(CONFIG_PPC) += arch/powerpc/lib/ppcstring.o
-ifeq ($(ARCH),arm)
-EXT_SOBJ-$(CONFIG_USE_ARCH_MEMSET) += arch/arm/lib/memset.o
+ifneq ($(CONFIG_ARM)$(CONFIG_RISCV),)
+EXT_SOBJ-$(CONFIG_USE_ARCH_MEMSET) += arch/$(ARCH)/lib/memset.o
 endif
 
 # Create a list of object files to be compiled