zlib: do not build POWER8 code on 32-bit PowerPC

zlib-ng decides whether to build its POWER8 and POWER9 sources from a
probe that compiles getauxval(AT_HWCAP2) & PPC_FEATURE2_ARCH_2_07 and
nothing else, so it accepts any target whose libc has getauxval. On
mpc85xx that offers POWER8 to an e500v2 and the build fails:

  adler32_power8.c:126:13: error: '__builtin_vsx_lxvw4x_v16qi' requires
  the '-mvsx' option

POWER8 is ISA 2.07 and POWER9 is ISA 3.0, 64-bit server ISAs that no
32-bit PowerPC in the tree implements, so turn both off for
ARCH=powerpc. powerpc64 keeps them, where they build and zlib-ng gates
them on HWCAP2 at runtime.

Fixes: b6ab56871d ("zlib: switch to zlib-ng 2.3.3 in zlib-compatible mode")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/libs/zlib/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=zlib
 PKG_VERSION:=2.3.3
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://github.com/zlib-ng/zlib-ng.git
@@ -66,6 +66,15 @@ CMAKE_OPTIONS += \
 	-DZLIB_COMPAT=ON \
 	-DBUILD_TESTING=OFF
 
+# POWER8 and POWER9 are 64-bit server ISAs; zlib-ng enables them from a probe
+# that only looks for getauxval and PPC_FEATURE2_ARCH_2_07, so it offers them
+# on e500 and PPC464 as well, where the compiler has no VSX to emit.
+ifeq ($(ARCH),powerpc)
+CMAKE_OPTIONS += \
+	-DWITH_POWER8=OFF \
+	-DWITH_POWER9=OFF
+endif
+
 define Build/InstallDev
 	mkdir -p $(1)/usr/include
 	$(CP)	$(PKG_INSTALL_DIR)/usr/include/{zconf,zlib,zlib_name_mangling}.h \