Distribute a gunzip.pl script

gunzip isn't reliably available on Windows, but IO::Uncompress::Gunzip should
be.

Suggested by Quietust.

CMake/DownloadFile.cmake

@@ -31,7 +31,9 @@ function(download_file_unzip URL ZIP_TYPE ZIP_DEST ZIP_MD5 UNZIP_DEST UNZIP_MD5)
     if(EXISTS "${ZIP_DEST}")
       message("* Decompressing ${FILENAME}")
       if("${ZIP_TYPE}" STREQUAL "gz")
-        execute_process(COMMAND gunzip --force "${ZIP_DEST}")
+        execute_process(COMMAND
+          "${PERL_EXECUTABLE}" "${CMAKE_SOURCE_DIR}/depends/gunzip.pl"
+          "${ZIP_DEST}" --force)
       else()
         message(SEND_ERROR "Unknown ZIP_TYPE: ${ZIP_TYPE}")
       endif()

depends/gunzip.pl

@@ -0,0 +1,21 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+
+use IO::Uncompress::Gunzip qw(gunzip $GunzipError);
+
+my %args = map { $_ => 1 } @ARGV;
+
+my $in_file = $ARGV[0] or die "no input file";
+# remove extension
+(my $out_file = $in_file) =~ s{\.[^.]+$}{};
+
+if (! -f $in_file) {
+    die "input file does not exist: \"$in_file\"\n";
+}
+if (-f $out_file and !exists($args{'--force'})) {
+    die "output file exists, not overwriting: \"$out_file\"";
+}
+
+gunzip $in_file => $out_file or die "gunzip failed: $GunzipError\n";