gh-106118: Add O_CLOEXEC preprocessor guard (#106120)

Author: erlend-aasland

Misc/NEWS.d/next/Build/2023-06-26-21-56-29.gh-issue-106118.0cCfhl.rst

@@ -0,0 +1,2 @@
+Fix compilation for platforms without :data:`!O_CLOEXEC`. The issue was
+introduced with Python 3.12b1 in :gh:`103295`. Patch by Erlend Aasland.

Python/sysmodule.c

@@ -2277,7 +2277,10 @@ PyAPI_FUNC(int) PyUnstable_PerfMapState_Init(void) {
     char filename[100];
     pid_t pid = getpid();
     // Use nofollow flag to prevent symlink attacks.
-    int flags = O_WRONLY | O_CREAT | O_APPEND | O_NOFOLLOW | O_CLOEXEC;
+    int flags = O_WRONLY | O_CREAT | O_APPEND | O_NOFOLLOW;
+#ifdef O_CLOEXEC
+    flags |= O_CLOEXEC;
+#endif
     snprintf(filename, sizeof(filename) - 1, "/tmp/perf-%jd.map",
                 (intmax_t)pid);
     int fd = open(filename, flags, 0600);