package/libnss: fix powerpc altivec build failure

NSS_DISABLE_ALTIVEC variable has been introduced into libnss so let's
use it to prevent Altivec build failure on PowerPc by passing
NSS_DISABLE_ALTIVEC=1 if BR2_POWERPC_CPU_HAS_ALTIVEC is not 'y'.

Fixes:
http://autobuild.buildroot.net/results/957/957cec911bcd68a18418ad02f13e7e3001521c59/
http://autobuild.buildroot.net/results/6a1/6a1578619a477e1605fe152070f004b662f1d839/

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libnss/libnss.mk

@@ -50,6 +50,11 @@ LIBNSS_BUILD_VARS = \
 	OS_TEST=$(BR2_PACKAGE_LIBNSS_ARCH) \
 	NSS_ENABLE_WERROR=0
 
+ifeq ($(BR2_POWERPC_CPU_HAS_ALTIVEC),)
+# Disable Altivec if not supported
+LIBNSS_BUILD_VARS += NSS_DISABLE_ALTIVEC=1
+endif
+
 ifeq ($(BR2_ARCH_IS_64),y)
 # MIPS64 n32 is treated as a 32-bit architecture by libnss.
 # See: https://bugzilla.mozilla.org/show_bug.cgi?id=1010730