tools/ocaml: Bump minimum version to OCaml 4.05

Char.lowercase got removed in OCaml 5.0 (it has been deprecated since 2014),
and doesn't build any more.

Char.lowercase_ascii has existed since OCaml 4.03, so that is the new
minimum version for oxenstored.

However, OCaml 4.05 is the oldest new-enough version found in common distros,
so pick this as a baseline.

Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
[Update CHANGELOG.md]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Changed
  - Changed flexible array definitions in public I/O interface headers to not
    use "1" as the number of array elements.
+ - The minimum supported OCaml toolchain version is now 4.05
  - On x86:
    - HVM PIRQs are disabled by default.
    - Reduce IOMMU setup time for hardware domain.

tools/configure

@@ -6836,7 +6836,7 @@ else
                      -e 's/[^0-9]//g'`
 
 
-  ax_compare_version_B=`echo "4.02.0" | sed -e 's/\([0-9]*\)/Z\1Z/g' \
+  ax_compare_version_B=`echo "4.05.0" | sed -e 's/\([0-9]*\)/Z\1Z/g' \
                      -e 's/Z\([0-9]\)Z/Z0\1Z/g' \
                      -e 's/Z\([0-9][0-9]\)Z/Z0\1Z/g' \
                      -e 's/Z\([0-9][0-9][0-9]\)Z/Z0\1Z/g' \

tools/configure.ac

@@ -336,7 +336,7 @@ AS_IF([test "x$ocamltools" = "xy"], [
             AC_MSG_ERROR([Ocaml tools enabled, but missing ocamlopt or ocamlfind])])
         ocamltools="n"
     ], [
-        AX_COMPARE_VERSION([$OCAMLVERSION], [lt], [4.02.0], [
+        AX_COMPARE_VERSION([$OCAMLVERSION], [lt], [4.05.0], [
             AS_IF([test "x$enable_ocamltools" = "xyes"], [
                 AC_MSG_ERROR([Your version of OCaml: $OCAMLVERSION is not supported])])
             ocamltools="n"

tools/ocaml/xenstored/disk.ml

@@ -30,7 +30,7 @@ let undec c =
   | _          -> raise (Failure "undecify")
 
 let unhex c =
-  let c = Char.lowercase c in
+  let c = Char.lowercase_ascii c in
   match c with
   | '0' .. '9' -> (Char.code c) - (Char.code '0')
   | 'a' .. 'f' -> (Char.code c) - (Char.code 'a') + 10