--- Source/WebCore/css/makegrammar.pl.orig	2017-06-16 14:46:36.000000000 +0200
+++ Source/WebCore/css/makegrammar.pl	2020-09-18 22:59:10.000000000 +0200
@@ -73,23 +73,7 @@
 }
 
 my $fileBase = File::Spec->join($outputDir, $filename);
-system("$bison -d -p $symbolsPrefix $grammarFilePath -o $fileBase.cpp");
-
-open HEADER, ">$fileBase.h" or die;
-print HEADER << "EOF";
-#ifndef CSSGRAMMAR_H
-#define CSSGRAMMAR_H
-EOF
-
-open HPP, "<$fileBase.cpp.h" or open HPP, "<$fileBase.hpp" or die;
-while (<HPP>) {
-    print HEADER;
-}
-close HPP;
-
-print HEADER "#endif\n";
-close HEADER;
-
-unlink("$fileBase.cpp.h");
-unlink("$fileBase.hpp");
+my @bisonCommand = ($bison, "--defines=$fileBase.h", "-p", $symbolsPrefix, $grammarFilePath, "-o", "$fileBase.cpp");
+push @bisonCommand, "--no-lines" if $^O eq "MSWin32"; # Work around bug in bison >= 3.0 on Windows where it puts backslashes into #line directives.
+system(@bisonCommand) == 0 or die;