[clang] [flang] [Flang][Driver] Enable the global-isel option (PR #177188)

[Tarun Prabhu via cfe-commits]

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@@ -0,0 +1,8 @@
+! -flto passes along an explicit GlobalISel flag.
+! RUN: %flang --target=aarch64-linux-gnu -### %s -flto -fglobal-isel 2> %t
+! RUN: FileCheck --check-prefix=CHECK-GISEL < %t %s
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tarunprabhu wrote:

Could stderr just be piped to FileCheck here? If so, our SSD's might appreciate it ;-)

```suggestion
! RUN: %flang --target=aarch64-linux-gnu -### %s -flto -fglobal-isel 2>&1 \
! RUN:     | FileCheck --check-prefix=CHECK-GISEL %s
```

https://github.com/llvm/llvm-project/pull/177188