Add flag to postgrest.cabal to disable collecting coverage data

postgrest.cabal

@@ -24,6 +24,11 @@ flag dev
   manual:      True
   description: Development flags
 
+flag hpc
+  default:     True
+  manual:      True
+  description: Enable HPC (dev only)
+
 library
   default-language:   Haskell2010
   default-extensions: OverloadedStrings
@@ -92,18 +97,20 @@ library
                     , wai-extra                 >= 3.0.19 && < 3.2
                     , wai-logger                >= 2.3.2
                     , wai-middleware-static     >= 0.8.1 && < 0.10
+                      -- -fno-spec-constr may help keep compile time memory use in check,
+                      --   see https://gitlab.haskell.org/ghc/ghc/issues/16017#note_219304
+                      -- -optP-Wno-nonportable-include-path
+                      --   prevents build failures on case-insensitive filesystems (macos),
+                      --   see https://github.com/commercialhaskell/stack/issues/3918
+  ghc-options:        -Werror -Wall -fwarn-identities
+                      -fno-spec-constr -optP-Wno-nonportable-include-path
+
   if flag(dev)
-    ghc-options: -O0 -Werror -Wall -fwarn-identities
-                 -fno-spec-constr -optP-Wno-nonportable-include-path
-                 -fhpc -hpcdir .hpc
+    ghc-options: -O0
+    if flag(hpc)
+      ghc-options: -fhpc -hpcdir .hpc
   else
-    ghc-options: -O2 -Werror -Wall -fwarn-identities
-                 -fno-spec-constr -optP-Wno-nonportable-include-path
-          -- -fno-spec-constr may help keep compile time memory use in check,
-          --   see https://gitlab.haskell.org/ghc/ghc/issues/16017#note_219304
-          -- -optP-Wno-nonportable-include-path
-          --   prevents build failures on case-insensitive filesystems (macos),
-          --   see https://github.com/commercialhaskell/stack/issues/3918
+    ghc-options: -O2
 
 executable postgrest
   default-language:   Haskell2010
@@ -131,16 +138,17 @@ executable postgrest
                     , time                >= 1.6 && < 1.11
                     , wai                 >= 3.2.1 && < 3.3
                     , warp                >= 3.2.12 && < 3.4
-  if flag(dev)
-    ghc-options:      -threaded -rtsopts "-with-rtsopts=-N -I2"
-                      -O0 -Werror -Wall -fwarn-identities
-                      -fno-spec-constr -optP-Wno-nonportable-include-path
-                      -fhpc -hpcdir .hpc
-  else
-    ghc-options:      -threaded -rtsopts "-with-rtsopts=-N -I2"
+  ghc-options:        -threaded -rtsopts "-with-rtsopts=-N -I2"
                       -O2 -Werror -Wall -fwarn-identities
                       -fno-spec-constr -optP-Wno-nonportable-include-path
 
+  if flag(dev)
+    ghc-options: -O0
+    if flag(hpc)
+      ghc-options: -fhpc -hpcdir .hpc
+  else
+    ghc-options: -O2
+
   if !os(windows)
     build-depends: unix
     other-modules: UnixSocket