Stop intercepting forkpty(3) and openpty(3) on NetBSD

[krytarowski]

Summary

forkpty(3) and openpty(3) are part of -lutil and we don't intend to reimplement
this system library in sanitizers. Everybody using these functions will need to use
a precompiled library against MSan or other desired sanitizer.

Restrict these functions to Linux-only.

Sponsored by <The NetBSD Foundation>

[krytarowski]

This also covers FreeBSD.

lib/msan/msan_interceptors.cc

 INTERCEPTOR(int, fork, void) {
   ENSURE_MSAN_INITED();
   BeforeFork();
   int pid = REAL(fork)();
   AfterFork();
   return pid;
 }
 
+// NetBSD ships with openpty(3) in -lutil, that needs to be prebuilt explicitly
+// with MSan.
+#if SANITIZER_LINUX
 INTERCEPTOR(int, openpty, int *amaster, int *aslave, char *name,
             const void *termp, const void *winp) {
   ENSURE_MSAN_INITED();
   InterceptorScope interceptor_scope;
   int res = REAL(openpty)(amaster, aslave, name, termp, winp);
   if (!res) {
     __msan_unpoison(amaster, sizeof(*amaster));
     __msan_unpoison(aslave, sizeof(*aslave));
   }
   return res;
 }
+#define MSAN_MAYBE_INTERCEPT_OPENPTY INTERCEPT_FUNCTION(openpty)
+#else
+#define MSAN_MAYBE_INTERCEPT_OPENPTY
+#endif
 
+// NetBSD ships with forkpty(3) in -lutil, that needs to be prebuilt explicitly
+// with MSan.
+#if SANITIZER_LINUX
 INTERCEPTOR(int, forkpty, int *amaster, char *name, const void *termp,
             const void *winp) {
   ENSURE_MSAN_INITED();
   InterceptorScope interceptor_scope;
   int res = REAL(forkpty)(amaster, name, termp, winp);
   if (res != -1)
     __msan_unpoison(amaster, sizeof(*amaster));
   return res;
 }
+#define MSAN_MAYBE_INTERCEPT_FORKPTY INTERCEPT_FUNCTION(forkpty)
+#else
+#define MSAN_MAYBE_INTERCEPT_FORKPTY
+#endif
 
 struct MSanInterceptorContext {
   bool in_interceptor_scope;
 };
 
 namespace __msan {
 
 int OnExit() {
#if SANITIZER_NETBSD
   INTERCEPT_FUNCTION(__libc_thr_keycreate);
 #endif
 
   INTERCEPT_FUNCTION(pthread_join);
   INTERCEPT_FUNCTION(tzset);
   INTERCEPT_FUNCTION(__cxa_atexit);
   INTERCEPT_FUNCTION(shmat);
   INTERCEPT_FUNCTION(fork);
-  INTERCEPT_FUNCTION(openpty);
-  INTERCEPT_FUNCTION(forkpty);
+  MSAN_MAYBE_INTERCEPT_OPENPTY;
+  MSAN_MAYBE_INTERCEPT_FORKPTY;
 
   inited = 1;
 }
 } // namespace __msan