Dynamically link compiler executable.

DDlog used to rely on static linking to reduce runtime dependencies.
Unfortunately, this no longer works well on recent Ubuntu and Fedora
releases (see #1051).  The problem appears to be in the `unix` Haskell
package, which may still load dynamic libraries (in particular glibc)
using `dlopen` when using static linking.  As far as I can tell it uses
older versions of Linux static libraries, which require some deprecated
libc symbols (specifically `__xmnod`).  This will probably get fixed
eventually, but overall static linking probably was not a good idea, so
we switch to the more standard dynamic linking method.

package.yaml

@@ -48,7 +48,7 @@ dependencies:
 library:
   source-dirs: src
   ghc-options:
-  - -optl-static
+  # - -optl-static
   - -optl-pthread
   - -Wall
   - -Werror
@@ -66,7 +66,7 @@ executables:
               - -threaded
               - -rtsopts
               - -with-rtsopts=-N
-              - -optl-static
+              # - -optl-static
               - -optl-pthread
               - -Wall
               - -Werror
@@ -91,7 +91,7 @@ executables:
               - -threaded
               - -rtsopts
               - -with-rtsopts=-N
-              - -optl-static
+              # - -optl-static
               - -Wall
               - -Werror
       else: