Add tool/missing-baseruby.bat, used when BASERUBY not available

Previously, the embedded semicolon in BASERUBY if BASERUBY is
not available breaks tarball builds without BASERUBY when using
OpenBSD make, due to the inability to escape MFLAGS correctly.
This moves the same BASERUBY code into a separate file, avoiding
the MFLAGS quoting issue.

BASERUBY must be passed to build-ext because it is required
by ripper since the introduction of lrama.

Fixes [Bug #19683]

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

configure.ac

@@ -89,7 +89,7 @@ AS_IF([test "$HAVE_BASERUBY" != no -a "`RUBYOPT=- $BASERUBY --disable=gems -e 'p
 ])
 AS_IF([test "$HAVE_BASERUBY" = no], [
     AS_IF([test "$cross_compiling" = yes], [AC_MSG_ERROR([executable host ruby is required for cross-compiling])])
-    BASERUBY="echo executable host ruby is required.  use --with-baseruby option.; false"
+    BASERUBY=$srcdir/tool/missing-baseruby.bat
 ])
 AC_SUBST(BASERUBY)
 AC_SUBST(HAVE_BASERUBY)

tool/missing-baseruby.bat

@@ -0,0 +1,5 @@
+: "
+@echo off
+: "
+echo executable host ruby is required.  use --with-baseruby option.
+exit 1