Drop support for native compilation on 32-bit Cygwin

* configure.ac (cygwin32-native-compilation): New option.
[i686-pc-cygwin]: Don't allow native compilation unless that
option is specified.  (Bug#50666)

configure.ac

@@ -485,6 +485,7 @@ OPTION_DEFAULT_ON([zlib],[don't compile with zlib decompression support])
 OPTION_DEFAULT_ON([modules],[don't compile with dynamic modules support])
 OPTION_DEFAULT_ON([threads],[don't compile with elisp threading support])
 OPTION_DEFAULT_OFF([native-compilation],[compile with Emacs Lisp native compiler support])
+OPTION_DEFAULT_OFF([cygwin32-native-compilation],[use native compilation on 32-bit Cygwin])
 
 AC_ARG_WITH([file-notification],[AS_HELP_STRING([--with-file-notification=LIB],
  [use a file notification library (LIB one of: yes, inotify, kqueue, gfile, w32, no)])],
@@ -3814,6 +3815,16 @@ source on this site:
 HAVE_NATIVE_COMP=no
 LIBGCCJIT_LIBS=
 LIBGCCJIT_CFLAGS=
+if test "$canonical" = i686-pc-cygwin; then
+  if test "${with_cygwin32_native_compilation}" = yes; then
+    with_native_compilation=yes
+  elif test "${with_native_compilation}" != no; then
+    AC_MSG_ERROR([Native compilation is not supported on 32-bit Cygwin.
+If you really want to try it anyway, use the configure option
+'--with-cygwin32-native-compilation'.])
+  fi
+fi
+
 if test "${with_native_compilation}" != "no"; then
     if test "${HAVE_PDUMPER}" = no; then
        AC_MSG_ERROR(['--with-native-compilation' requires '--with-dumping=pdumper'])