Ensure BASERUBY when cross-compiling

configure.ac

@@ -76,6 +76,7 @@ AS_IF([test "$HAVE_BASERUBY" != no -a "`RUBYOPT=- $BASERUBY --disable=gems -e 'p
     HAVE_BASERUBY=no
 ])
 AS_IF([test "$HAVE_BASERUBY" = no], [
+    AS_IF([test "$cross_compiling" = yes], [AC_MSG_ERROR([executable host ruby is required for cross-compiling])])
     BASERUBY="echo executable host ruby is required.  use --with-baseruby option.; false"
 ])
 AC_SUBST(BASERUBY)

win32/Makefile.sub

@@ -24,6 +24,14 @@ REVISION_FORCE = PHONY
 
 !ifndef CROSS_COMPILING
 CROSS_COMPILING = no
+!else if "$(CROSS_COMPILING)" == "yes"
+! if "$(HAVE_BASERUBY)" != "yes"
+!   error executable host ruby is required for cross-compiling
+! endif
+!else
+! if "$(CROSS_COMPILING)" != "no"
+!   error Bad CROSS_COMPILING
+! endif
 !endif
 !ifndef win_srcdir
 win_srcdir = $(srcdir)/win32