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

[Abid Qadeer via cfe-commits]

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@@ -614,3 +614,28 @@ nvfortran defines `-fast` as
  - `-Mcache_align`: there is no equivalent flag in Flang or Clang.
  - `-Mflushz`: flush-to-zero mode - when `-ffast-math` is specified, Flang will
    link to `crtfastmath.o` to ensure denormal numbers are flushed to zero.
+
+
+## FCC_OVERRIDE_OPTIONS
+
+The environment variable `FCC_OVERRIDE_OPTIONS` can be used to apply a list of
+edits to the input argument lists. The value of this environment variable is
----------------
abidh wrote:

It does not effect the options added by the configuration files. The behavior is consistent with clang and `CCC_OVERRIDE_OPTIONS`.  I added a line in the documentation for it.

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