[flang] [llvm] [flang] Add HOSTNM runtime and lowering intrinsics implementation (PR #131910)

[Eugene Epshteyn via llvm-commits]

================
@@ -263,4 +263,39 @@ std::int32_t RTNAME(GetCwd)(
   return status;
 }
 
+std::int32_t RTNAME(Hostnm)(
+    const Descriptor &res, const char *sourceFile, int line) {
+  Terminator terminator{sourceFile, line};
+
+  RUNTIME_CHECK(terminator, IsValidCharDescriptor(&res));
+
+  char buf[256];
+  std::int32_t status{0};
+
+#ifdef _WIN32
+
+  DWORD dwSize{sizeof(buf)};
+
+  // Note: Winsock has gethostname(), but use Win32 API GetComputerNameEx(),
+  // in order to avoid adding dependency on Winsock.
+  if (!GetComputerNameEx(ComputerNameDnsHostname, buf, &dwSize)) {
+    status = GetLastError();
+  }
+
+#else
+
+  if (gethostname(buf, sizeof(buf)) < 0) {
+    status = errno;
+  }
+
+#endif
+
+  if (status == 0) {
+    std::int64_t strLen{StringLength(buf)};
+    status = CopyCharsToDescriptor(res, buf, strLen);
+  }
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eugeneepshteyn wrote:

Should be handled now via initial `FillWithSpaces()`.

https://github.com/llvm/llvm-project/pull/131910