curl: restore SOURCE_DATE_EPOCH

lld from llvm 18 respects it. We are doing our own PE cleaning for now,
but this could eventually take over (once `debian:testing` switches to
18 and possibly `ld` also implements it.)

https://releases.llvm.org/18.1.0/tools/lld/docs/ReleaseNotes.html#coff-improvements
llvm/llvm-project#81326

Author: vszakats

curl-autotools.sh

@@ -16,6 +16,15 @@ _VER="$1"
 
   rm -r -f "${_PKGDIR:?}" "${_BLDDIR:?}"
 
+  readonly _ref='CHANGES'
+
+  case "${_HOST}" in
+    bsd|mac) unixts="$(TZ=UTC stat -f '%m' "${_ref}")";;
+    *)       unixts="$(TZ=UTC stat -c '%Y' "${_ref}")";;
+  esac
+
+  export SOURCE_DATE_EPOCH="${unixts}"
+
   # Build
 
   [ -f 'configure' ] || autoreconf --force --install

curl-cmake.sh

@@ -19,6 +19,15 @@ _VER="$1"
 
   [ "${CW_DEV_INCREMENTAL:-}" != '1' ] && rm -r -f "${_PKGDIR:?}" "${_BLDDIR:?}"
 
+  readonly _ref='CHANGES'
+
+  case "${_HOST}" in
+    bsd|mac) unixts="$(TZ=UTC stat -f '%m' "${_ref}")";;
+    *)       unixts="$(TZ=UTC stat -c '%Y' "${_ref}")";;
+  esac
+
+  export SOURCE_DATE_EPOCH="${unixts}"
+
   # Build
 
   options=''

curl-pkg.sh

@@ -8,9 +8,8 @@
 {
   # Make steps for determinism
 
-  readonly _ref='CHANGES'
-
   # Show the reference timestamp in UTC.
+  # shellcheck disable=SC2154
   case "${_HOST}" in
     bsd|mac) TZ=UTC stat -f '%N: %Sm' -t '%Y-%m-%d %H:%M' "${_ref}";;
     *)       TZ=UTC stat -c '%n: %y' "${_ref}";;