fix suppression of info installation

blanking INFO_DEPS suffices to prevent attempts to rebuild the docs,
but does not reliably suppress their installation. blanking infodir
does the latter. there are other methods that work too but this seems
to be the simplest.

litecross/Makefile

@@ -15,7 +15,7 @@ MUSL_CONFIG = CC="$(XGCC)" LIBCC="../obj_toolchain/$(TARGET)/libgcc/libgcc.a" --
 
 -include config.mak
 
-MAKE += INFO_DEPS=
+MAKE += INFO_DEPS= infodir=
 MAKE += ac_cv_prog_lex_root=lex.yy.c
 
 FULL_TOOLCHAIN_CONFIG = $(TOOLCHAIN_CONFIG) \