sigpipe tests: Fix -Wanalyzer-unsafe-call-within-signal-handler warning

[Bruno Haible]

This warning can be fixed like the one in test-raise.c:

test-sigpipe.c:34:3: warning: call to 'exit' from within signal handler 
[CWE-479] [-Wanalyzer-unsafe-call-within-signal-handler]


2023-09-04  Bruno Haible  <bruno@clisp.org>

        sigpipe tests: Fix -Wanalyzer-unsafe-call-within-signal-handler warning.
        * tests/test-sigpipe.c (handler): Invoke _exit, not exit.
        * tests/test-raise.c (handler): Update comments after 2020-11-25 change.

diff --git a/tests/test-raise.c b/tests/test-raise.c
index 97be64dd2c..38088a53ea 100644
--- a/tests/test-raise.c
+++ b/tests/test-raise.c
@@ -26,9 +26,9 @@ SIGNATURE_CHECK (raise, int, (int));
 
 #include "macros.h"
 
-/* It is safe to use _Noreturn here: exit() never returns, and GCC knows that
-   exit() is a non-returning function, even on platforms where its declaration
-   in <stdlib.h> does not have the 'noreturn' attribute.  */
+/* It is safe to use _Noreturn here: _exit() never returns, and GCC knows that
+   _exit() is a non-returning function, even on platforms where its declaration
+   in <unistd.h> does not have the 'noreturn' attribute.  */
 static _Noreturn void
 handler (_GL_UNUSED int sig)
 {
diff --git a/tests/test-sigpipe.c b/tests/test-sigpipe.c
index ab8745b3bd..efff9d55f8 100644
--- a/tests/test-sigpipe.c
+++ b/tests/test-sigpipe.c
@@ -31,7 +31,7 @@ int s = SIGPIPE;
 static void
 handler (int sig)
 {
-  exit (0);
+  _exit (0);
 }
 
 int