mbedtls: add --function-sections and --data-sections to CFLAGS

This allows binaries that links these libraries statically to be reduced
by using --gc-sections on link

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/libs/mbedtls/Makefile

@@ -48,6 +48,8 @@ endef
 
 PKG_INSTALL:=1
 
+TARGET_CFLAGS += -ffunction-sections -fdata-sections
+
 CMAKE_OPTIONS += \
 	-DCMAKE_BUILD_TYPE:String="Release" \
 	-DUSE_SHARED_MBEDTLS_LIBRARY:Bool=ON \