work around a threading bug in mksquashfs4 by limiting the number of threads to 1

SVN-Revision: 17146

include/image.mk

@@ -29,7 +29,7 @@ endif
 
 ifneq ($(USE_SQUASHFS4),)
 MKSQUASHFS_CMD := $(STAGING_DIR_HOST)/bin/mksquashfs4
-SQUASHFS_OPTS  := -lzma
+SQUASHFS_OPTS  := -lzma -processors 1
 else
 MKSQUASHFS_CMD := $(STAGING_DIR_HOST)/bin/mksquashfs-lzma
 endif