Drop -fast-llvm

`-fast-llvm` bypasses the mangler. We *could* do this if we had `-fast-llvm` *and* `-fno-plt`; however `-fno-plt` is only supported in the `clang` frontend, and essentially emits `nonlazybind` function attributes. LLVM does not guarantee that all architecture lowering backends respect that attribute and as such this would only work on `x86_64`, and on `aarch64` if passed `-aarch64-enable-nonlazybind`. Arm32 backends don't seem to support this attribute at all.

Fixes #621

Author: angerman

compiler/ghc/default.nix

@@ -102,9 +102,6 @@ let
     GhcRtsHcOpts += -fPIC
   '' + stdenv.lib.optionalString targetPlatform.useAndroidPrebuilt ''
     EXTRA_CC_OPTS += -std=gnu99
-  '' + stdenv.lib.optionalString useLLVM ''
-    GhcStage2HcOpts += -fast-llvm
-    GhcLibHcOpts += -fast-llvm
   '' + stdenv.lib.optionalString (!enableTerminfo) ''
     WITH_TERMINFO=NO
   ''