execute tests: Fix compilation error on native Windows

[Bruno Haible]

A testdir for module 'execute' fails to compile on mingw:

../../gltests/test-execute-main.c: In function ‘main’:
../../gltests/test-execute-main.c:70:11: error: ‘SIGPIPE’ undeclared (first use 
in this function); did you mean ‘SIGFPE’?
   70 |   signal (SIGPIPE, SIG_DFL);
      |           ^~~~~~~

This patch fixes it.


2023-04-20  Bruno Haible  <bruno@clisp.org>

        execute tests: Fix compilation error on mingw (regression 2023-01-17).
        * tests/test-execute-main.c (main): Don't use SIGPIPE if it's not
        defined.

diff --git a/tests/test-execute-main.c b/tests/test-execute-main.c
index 2088408756..cb799cf883 100644
--- a/tests/test-execute-main.c
+++ b/tests/test-execute-main.c
@@ -67,7 +67,9 @@ main (int argc, char *argv[])
      GNU make 4.4: <https://savannah.gnu.org/bugs/index.php?63307>.
      It causes the tests 3 and 4 to fail.  Work around it by resetting
      the signal handler for SIGPIPE to the default.  */
+  #ifdef SIGPIPE
   signal (SIGPIPE, SIG_DFL);
+  #endif
 
   switch (test)
     {