[llvm] [clang] [clang-tools-extra] [flang] [flang] GETLOG runtime and extension implementation: get login username (PR #74628)

[Peter Klausler via llvm-commits]

================
@@ -37,5 +79,34 @@ void FORTRAN_PROCEDURE_NAME(getarg)(
   (void)RTNAME(GetCommandArgument)(
       n, &value, nullptr, nullptr, __FILE__, __LINE__);
 }
+
+// CALL GETLOG(USRNAME)
+void FORTRAN_PROCEDURE_NAME(getlog)(std::int8_t *arg, std::int64_t length) {
+  const int nameMaxLen{LOGIN_NAME_MAX + 1};
+  char str[nameMaxLen];
+
+  int error{getlogin_r(str, nameMaxLen)};
+  Terminator terminator{__FILE__, __LINE__};
+  if (error != 0) {
+    // if there is error, then get username from environment variable
+#ifdef _WIN32
+    const int charLen = 9;
----------------
klausler wrote:

`static const char envName[]{"USERNAME"};`

https://github.com/llvm/llvm-project/pull/74628