drop ghc_compiler and use pkg_name in devel description

ghc-unordered-containers.spec

@@ -30,13 +30,13 @@ amortized, but remains valid even if structures are shared.
 
 %package devel
 Summary:        Haskell %{pkg_name} library development files
-Requires:       %{ghc_compiler}
-Requires(post): %{ghc_compiler}
-Requires(postun): %{ghc_compiler}
+Requires:       ghc-compiler = %{ghc_version}
+Requires(post): ghc-compiler = %{ghc_version}
+Requires(postun): ghc-compiler = %{ghc_version}
 Requires:       %{name} = %{version}-%{release}
 
 %description devel
-This package provides the Haskell unordered-containers library
+This package provides the Haskell %{pkg_name} library
 development files.
 
 %prep