When -fsplit-sections is passed to GHC, pass -ffunction-sections
-fdata-sections to gcc/clang when building C/C++. Previously,
-fsplit-sections was only respected by the NCG/LLVM backends, but not
the unregisterised backend; the GHC driver did not pass
-fdata-sections and -ffunction-sections to the C compiler, which
resulted in excessive executable sizes.

Fixes #23381.

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Metric Decrease:
    size_hello_artifact
    size_hello_unicode
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(cherry picked from commit 02b1f91e)