nettle: disable assembler on ppc64

As of version 3.7, Nettle added PowerPC64 assembly for several
algorithms. Unfortunately, they cause build to fail due to ABI mismatch:

gcm-hash.o: ABI version 1 is not compatible with ABI version 2 output

Disable assembler when ppc64 and musl are used for now.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Acked-by: Rui Salvaterra <rsalvaterra@gmail.com>

package/libs/nettle/Makefile

@@ -44,7 +44,8 @@ CONFIGURE_ARGS += \
 	--enable-fat \
 	--disable-openssl \
 	--disable-documentation \
-	--enable-static
+	--enable-static \
+	$(if $(CONFIG_powerpc64), $(if $(CONFIG_USE_MUSL),--disable-assembler))
 
 ifeq ($(CONFIG_LIBNETTLE_MINI),y)
 CONFIGURE_ARGS += --enable-mini-gmp