bug#62450: 29.0.60; Skip failing tests on Cygwin with native compilation

[Ken Brown <kbrown@cornell.edu>]

On 3/26/2023 12:44 AM, Eli Zaretskii wrote:
> OK, but please add in both places comments explaining the reason, and
> in particular include there a pointer to etc/PROBLEMS.

Done.

> (I do wonder whether this is a good idea in the long run.  Native
> compilation is here to stay, so avoiding its testing for Cygwin might
> not be the best solution.  The PROBLEMS entry seems to imply that
> relatively simple measures, which the test suite could take, could
> avoid the fork failures, so my recommendation would be to try to find
> a better fix in the future, albeit not in Emacs 29.)

I agree, and I hope I can do it.  By the way, I've been experimenting 
with building the .eln files with ASLR enabled, via the following:

--- a/lisp/emacs-lisp/comp.el
+++ b/lisp/emacs-lisp/comp.el
@@ -186,8 +186,9 @@ native-comp-compiler-options
    :type '(repeat string)
    :version "28.1")

-(defcustom native-comp-driver-options (when (eq system-type 'darwin)
-                                        '("-Wl,-w"))
+(defcustom native-comp-driver-options
+  (cond ((eq system-type 'darwin) '("-Wl,-w"))
+        ((eq system-type 'cygwin) '("-Wl,-dynamicbase")))
    "Options passed verbatim to the native compiler's back-end driver.
  Note that not all options are meaningful; typically only the options
  affecting the assembler and linker are likely to be useful.

I've been building and running Emacs like this for a couple months and 
not doing any rebasing, and I haven't seen a single fork failure outside 
of the test suite.  So this might be the way to handle the problem in 
the long run.  But I still hope to figure out what's different about 
native compilation in the test suite.

Ken