[clang] [flang] [flang][driver] Introduce FCC_OVERRIDE_OPTIONS. (PR #140556)

[Kiran Chandramohan via cfe-commits]

================
@@ -111,6 +111,13 @@ int main(int argc, const char **argv) {
     }
   }
 
+  llvm::StringSet<> SavedStrings;
+  // Handle FCC_OVERRIDE_OPTIONS, used for editing a command line behind the
+  // scenes.
+  if (const char *OverrideStr = ::getenv("FCC_OVERRIDE_OPTIONS"))
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kiranchandramohan wrote:

```suggestion
  if (const char *overrideStr = ::getenv("FCC_OVERRIDE_OPTIONS"))
```

https://github.com/llvm/llvm-project/pull/140556