libnspr: only pass --{enable,disable}-thumb2 on ARM

Fixes http://autobuild.buildroot.net/results/dff3f851ee4c62067a0b231c683383ce8692b8b3

libnspr adds -marm to CFLAGS when passed --disable-thumb2, which is only
recognized by ARM cross compilers, so only use when building for ARM.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libnspr/libnspr.mk

@@ -16,11 +16,13 @@ LIBNSPR_CONF_OPT  = --host=$(GNU_HOST_NAME)
 LIBNSPR_CONF_OPT += --$(if $(BR2_ARCH_IS_64),en,dis)able-64bit
 LIBNSPR_CONF_OPT += --$(if $(BR2_INET_IPV6),en,dis)able-ipv6
 
+ifeq ($(BR2_arm),y)
 ifeq ($(BR2_cortex_a8)$(BR2_cortex_a9),y)
 LIBNSPR_CONF_OPT += --enable-thumb2
 else
 LIBNSPR_CONF_OPT += --disable-thumb2
 endif
+endif
 
 define LIBNSPR_STAGING_LIBNSPR_CONFIG_FIXUP
 	$(SED) "s,^prefix=.*,prefix=\'$(STAGING_DIR)/usr\',g" \