Let debugger handle process spawn errors on w32 (Bug#33016)

Since child_setup() is called between block_input()...unblock_input(),
when an error is signaled the Lisp debugger is prevented from
starting.  Therefore, let the callers signal the error instead (which
they already do for non-w32 platforms, just the error message needs an
update).
* src/callproc.c (child_setup) [WINDOWSNT]: Don't call
report_file_error here.
(call_process) [WINDOWNT]:
* src/process.c (create_process) [WINDOWSNT]: Call report_file_errno
here instead, after the unblock_input() call, same as for !WINDOWSNT.
* src/lisp.h (CHILD_SETUP_ERROR_DESC): New preprocessor define.  Flip
the containing ifndef DOS_NT branches so that it's ifdef DOS_NT.
* src/eval.c (when_entered_debugger): Remove.
(syms_of_eval) <internal-when-entered-debugger>: Define it as a Lisp
integer variable instead.
(maybe_call_debugger): Update comment.
* test/src/process-tests.el (make-process-w32-debug-spawn-error):
* test/src/callproc-tests.el (call-process-w32-debug-spawn-error): New
tests.

1 files changed, 6 insertions, 3 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 681efc3b52b..2915944ffec 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4480,11 +4480,14 @@ extern void syms_of_process (void);
 extern void setup_process_coding_systems (Lisp_Object);
 
 /* Defined in callproc.c.  */
-#ifndef DOS_NT
-# define CHILD_SETUP_TYPE _Noreturn void
-#else
+#ifdef DOS_NT
 # define CHILD_SETUP_TYPE int
+# define CHILD_SETUP_ERROR_DESC "Spawning child process"
+#else
+# define CHILD_SETUP_TYPE _Noreturn void
+# define CHILD_SETUP_ERROR_DESC "Doing vfork"
 #endif
+
 extern CHILD_SETUP_TYPE child_setup (int, int, int, char **, bool, Lisp_Object);
 extern void init_callproc_1 (void);
 extern void init_callproc (void);