A lot of packages do not work with GHC 9.0.1 by default since their
version constraint for packages from the standard library is too
restrictive. Adjust these version constrains to fix the build.

Only in b: _build
diff -upr a/bootstrap/bootstrap.py b/bootstrap/bootstrap.py
--- a/bootstrap/bootstrap.py	2021-11-17 20:24:56.563114540 +0100
+++ b/bootstrap/bootstrap.py	2021-11-17 20:13:30.311479911 +0100
@@ -147,6 +147,11 @@ def fetch_package(package: PackageName,
             shutil.copyfileobj(resp, cabal_file.open('wb'))
             verify_sha256(cabal_sha256, cabal_file)
 
+    if package == "ed25519":
+        subprocess_run(["sed", "-e", "s/ghc-prim ..*/ghc-prim >= 0.1,/", "-i", cabal_file], check=True)
+    elif package == "hackage-security":
+        subprocess_run(["sed", "-e", "s/template-haskell ..*/template-haskell >= 2.7,/", "-i", cabal_file], check=True)
+
     return (tarball, cabal_file)
 
 def read_bootstrap_info(path: Path) -> BootstrapInfo:
diff -upr a/cabal-install/cabal-install.cabal b/cabal-install/cabal-install.cabal
--- a/cabal-install/cabal-install.cabal	2021-11-05 00:16:33.000000000 +0100
+++ b/cabal-install/cabal-install.cabal	2021-11-17 20:17:03.488421095 +0100
@@ -209,7 +209,7 @@ library
         edit-distance >= 0.2.2 && < 0.3,
         exceptions,
         filepath   >= 1.4.0.0  && < 1.5,
-        hashable   >= 1.0      && < 1.4,
+        hashable   >= 1.0,
         HTTP       >= 4000.1.5 && < 4000.4,
         mtl        >= 2.0      && < 2.3,
         network-uri >= 2.6.0.2 && < 2.7,
diff -upr a/cabal-install-solver/cabal-install-solver.cabal b/cabal-install-solver/cabal-install-solver.cabal
--- a/cabal-install-solver/cabal-install-solver.cabal	2021-11-05 00:16:33.000000000 +0100
+++ b/cabal-install-solver/cabal-install-solver.cabal	2021-11-17 19:42:41.703460745 +0100
@@ -103,7 +103,7 @@ library
 
   build-depends:
     , array         >=0.4      && <0.6
-    , base          >=4.10     && <4.15
+    , base          >=4.10
     , binary        >=0.7.3    && <0.9
     , bytestring    >=0.10.6.0 && <0.12
     , Cabal         ^>=3.7