treewide: fix *Flags

pkgs/applications/science/molecular-dynamics/gromacs/default.nix

@@ -1,4 +1,6 @@
-{ stdenv, fetchurl, cmake
+{ stdenv
+, fetchurl
+, cmake
 , singlePrec ? true
 , mpiEnabled ? false
 , fftw
@@ -6,7 +8,6 @@
 , perl
 }:
 
-
 stdenv.mkDerivation {
   name = "gromacs-2019.4";
 
@@ -19,18 +20,27 @@ stdenv.mkDerivation {
   buildInputs = [ fftw perl ]
   ++ (stdenv.lib.optionals mpiEnabled [ openmpi ]);
 
-  cmakeFlags = ''
-    ${if singlePrec then "-DGMX_DOUBLE=OFF" else "-DGMX_DOUBLE=ON -DGMX_DEFAULT_SUFFIX=OFF"}
-    ${if mpiEnabled then "-DGMX_MPI:BOOL=TRUE
-                          -DGMX_CPU_ACCELERATION:STRING=SSE4.1
-                          -DGMX_OPENMP:BOOL=TRUE
-                          -DGMX_THREAD_MPI:BOOL=FALSE"
-                     else "-DGMX_MPI:BOOL=FALSE" }
-  '';
+  cmakeFlags = (
+    if singlePrec then [
+      "-DGMX_DOUBLE=OFF"
+    ] else [
+      "-DGMX_DOUBLE=ON"
+      "-DGMX_DEFAULT_SUFFIX=OFF"
+    ]
+  ) ++ (
+    if mpiEnabled then [
+      "-DGMX_MPI:BOOL=TRUE"
+      "-DGMX_CPU_ACCELERATION:STRING=SSE4.1"
+      "-DGMX_OPENMP:BOOL=TRUE"
+      "-DGMX_THREAD_MPI:BOOL=FALSE"
+    ] else [
+      "-DGMX_MPI:BOOL=FALSE"
+    ]
+  );
 
   meta = with stdenv.lib; {
-    homepage    = "http://www.gromacs.org";
-    license     = licenses.gpl2;
+    homepage = "http://www.gromacs.org";
+    license = licenses.gpl2;
     description = "Molecular dynamics software package";
     longDescription = ''
       GROMACS is a versatile package to perform molecular dynamics,