[compiler-rt] [profile] Implement a non-mmap path when reading profile files from a non-local filesystem (PR #131177)

[Hubert Tong via llvm-commits]

================
@@ -258,6 +267,120 @@ COMPILER_RT_VISIBILITY FILE *lprofOpenFileEx(const char *ProfileName) {
   return f;
 }
 
+// Return 1 (true) if the file descriptor Fd represents a file that is on a
+// local filesystem, otherwise return 0.
+static int is_local_filesystem(int Fd) {
+#if defined(_AIX)
+  struct statfs Vfs;
+  if (fstatfs(Fd, &Vfs) != 0) {
+    PROF_ERR("%s: fstatfs(%d) failed: %s\n", __func__, Fd, strerror(errno));
+    return 0;
+  }
+
+  int Ret;
+  size_t BufSize = 2048u;
+  char *Buf;
+  int Tries = 3;
+  while (Tries--) {
+    Buf = malloc(BufSize);
+    Ret = mntctl(MCTL_QUERY, BufSize, Buf);
----------------
hubert-reinterpretcast wrote:

```suggestion
    // mntctl returns -1 if `Buf` is `NULL`.
    Ret = mntctl(MCTL_QUERY, BufSize, Buf);
```

https://github.com/llvm/llvm-project/pull/131177