Force building with ghc-9.6.5

The default makepkg configuration sets LDFLAGS but not LD.
GHC used to take this as its cue to select its own choice of LD.
However GHC would *not* check that its choice of LD supports LDFLAGS.
This is a problem for dependencies with C components, which get linked
using this LD.

A fix[1] for this has landed in ghc 9.6.5 on 2024-04-16, and ghc's
installed using the current ghcup HEAD (starting with 7a684ad[2]) will
have `--disable-ld-override` passed, which also fixes the issue.

[1] - https://gitlab.haskell.org/ghc/ghc/-/issues/24565
[2] - haskell/ghcup-hs#1032

PKGBUILD

@@ -21,6 +21,12 @@ pkgver() {
     git describe --tags --long | sed 's/^v//;s/\([^-]*-g\)/r\1/;s/-/./g'
 }
 
+prepare() {
+    cd "$pkgname"
+    stack config set resolver lts-22.19 # ghc-9.6.4
+    echo 'compiler: ghc-9.6.5' >> stack.yaml
+}
+
 build() {
     cd "${pkgname}"
     stack build