Fix static linking on MacOS by preventing '-optl-static' flag

The treatment of --executable-static means we pass `-optl-static` to GHC, which in turn just passes this to the linker. This flag can not work on macOS. Fully static linking is impossible as libSystem must be linked dynamically.

Thus here we disable this flag for macOS.

Author: angerman

Cabal/src/Distribution/Simple/GHC/Build/Link.hs

@@ -121,6 +121,14 @@ linkOrLoadComponent
               PD.ldOptions bi
                 ++ [ "-static"
                    | withFullyStaticExe lbi
+                   -- MacOS can not link fully statically.
+                   -- Only kernels can be linked fully statically. Everything
+                   -- linking against libSystem must link dynamically. Thus even
+                   -- if we link all dependencies statically, we must not pass
+                   -- '-optl-static', as that will cause the linker to try and
+                   -- fail.
+                   , let Platform _hostArch hostOS = hostPlatform lbi
+                      in hostOS /= OSX
                    ]
                 -- Pass extra `ld-options` given
                 -- through to GHC's linker.