emacs-28 6ba4e3b: Drop support for native compilation on 32-bit Cygwin

[Ken Brown]

branch: emacs-28
commit 6ba4e3b78c9ade565ebcb9fa0473c798e0bc0a7b
Author: Ken Brown <kbrown@cornell.edu>
Commit: Ken Brown <kbrown@cornell.edu>

    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 | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/configure.ac b/configure.ac
index e6ffea0..6bc194d 100644
--- a/configure.ac
+++ b/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'])