[flang] [clang] [flang][driver] deprecate manual usage of -lFortran_main (PR #79016)

[Andrzej Warzyński via cfe-commits]

================
@@ -1193,6 +1193,16 @@ static void addFortranMain(const ToolChain &TC, const ArgList &Args,
     return;
   }
 
+  const Driver &D = TC.getDriver();
+  const char *LinkFlag = "-lFortran_main";
+
+  // warn if -lFortran_main was already specified
+  for (const char *arg : CmdArgs) {
+    if (strncmp(arg, LinkFlag, strlen(LinkFlag)) == 0)
+      D.Diag(diag::warn_drv_deprecated_custom)
+          << LinkFlag << "see the flang driver documentation for correct usage";
----------------
banach-space wrote:

[nit] 
```suggestion
          << LinkFlag << "see the Flang driver documentation for correct usage";
```

https://github.com/llvm/llvm-project/pull/79016