merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/contrib/buildsystems/Generators.pm

@@ -0,0 +1,42 @@
+package Generators;
+require Exporter;
+
+use strict;
+use File::Basename;
+no strict 'refs';
+use vars qw($VERSION @AVAILABLE);
+
+our $VERSION = '1.00';
+our(@ISA, @EXPORT, @EXPORT_OK, @AVAILABLE);
+@ISA = qw(Exporter);
+
+BEGIN {
+    local(*D);
+    my $me = $INC{"Generators.pm"};
+    die "Couldn't find myself in \@INC, which is required to load the generators!" if ("$me" eq "");
+    $me = dirname($me);
+    if (opendir(D,"$me/Generators")) {
+        foreach my $gen (readdir(D)) {
+            next unless ($gen  =~ /\.pm$/);
+            require "${me}/Generators/$gen";
+            $gen =~ s,\.pm,,;
+            push(@AVAILABLE, $gen);
+        }
+        closedir(D);
+        my $gens = join(', ', @AVAILABLE);
+    }
+
+    push @EXPORT_OK, qw(available);
+}
+
+sub available {
+    return @AVAILABLE;
+}
+
+sub generate {
+    my ($gen, $git_dir, $out_dir, $rel_dir, %build_structure) = @_;
+    return eval("Generators::${gen}::generate(\$git_dir, \$out_dir, \$rel_dir, \%build_structure)") if grep(/^$gen$/, @AVAILABLE);
+    die "Generator \"${gen}\" is not available!\nAvailable generators are: @AVAILABLE\n";
+}
+
+1;