Submitted upstream:

  <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/9394>

From 6b218717ac85d6dc9104f470cac0b4fb594104f4 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 22 Nov 2022 15:23:50 +0100
Subject: [PATCH] m4/fp_leading_underscore.m4: Avoid implicit exit function
 declaration
Content-type: text/plain

And switch to a new-style function definition.

Fixes build issues with compilers that do not accept implicit function
declarations.
---
 m4/fp_leading_underscore.m4 | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/m4/fp_leading_underscore.m4 b/m4/fp_leading_underscore.m4
index fde57c7625..939cee3b69 100644
--- a/m4/fp_leading_underscore.m4
+++ b/m4/fp_leading_underscore.m4
@@ -32,17 +32,15 @@ struct nlist xYzzY1[] = {{"xYzzY1", 0},{0}};
 struct nlist xYzzY2[] = {{"_xYzzY2", 0},{0}};
 #endif
 
-int main(argc, argv)
-int argc;
-char **argv;
+int main(int argc, char **argv)
 {
 #if defined(HAVE_NLIST_H)
     if(nlist(argv[0], xYzzY1) == 0 && xYzzY1[0].n_value != 0)
-        exit(1);
+        return 1;
     if(nlist(argv[0], xYzzY2) == 0 && xYzzY2[0].n_value != 0)
-        exit(0);
+        return 0;
 #endif
-    exit(1);
+    return 1;
 }]])],[fptools_cv_leading_underscore=yes],[fptools_cv_leading_underscore=no],[fptools_cv_leading_underscore=no])
 ;;
 esac]);
diff -ur ghc-9.4.3.orig/configure ghc-9.4.3/configure
--- ghc-9.4.3.orig/configure	2022-11-03 04:46:32.000000000 +0100
+++ ghc-9.4.3/configure	2022-11-22 16:37:07.812512120 +0100
@@ -17095,17 +17101,15 @@
 struct nlist xYzzY2[] = {{"_xYzzY2", 0},{0}};
 #endif
 
-int main(argc, argv)
-int argc;
-char **argv;
+int main(int argc, char **argv)
 {
 #if defined(HAVE_NLIST_H)
     if(nlist(argv[0], xYzzY1) == 0 && xYzzY1[0].n_value != 0)
-        exit(1);
+        return 1;
     if(nlist(argv[0], xYzzY2) == 0 && xYzzY2[0].n_value != 0)
-        exit(0);
+        return 0;
 #endif
-    exit(1);
+    return 1;
 }
 _ACEOF
 if ac_fn_c_try_run "$LINENO"; then :