[linux-kernel] Fix duplicate symbols when built-in to kernel

contrib/linux-kernel/lib/zstd/Makefile

@@ -3,7 +3,16 @@ obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o
 
 ccflags-y += -O3
 
-zstd_compress-y := entropy_common.o fse_decompress.o zstd_common.o \
-				fse_compress.o huf_compress.o compress.o
-zstd_decompress-y := entropy_common.o fse_decompress.o zstd_common.o \
-				huf_decompress.o decompress.o
+# Object files unique to zstd_compress and zstd_decompress
+zstd_compress-y := fse_compress.o huf_compress.o compress.o
+zstd_decompress-y := huf_decompress.o decompress.o
+
+# These object files are shared between the modules.
+# Always add them to zstd_compress.
+# Unless both zstd_compress and zstd_decompress are built in
+# then also add them to zstd_decompress.
+zstd_compress-y += entropy_common.o fse_decompress.o zstd_common.o
+
+ifneq ($(CONFIG_ZSTD_COMPRESS)$(CONFIG_ZSTD_DECOMPRESS),yy)
+	zstd_decompress-y += entropy_common.o fse_decompress.o zstd_common.o
+endif