geninfo: Add workaround for MSYS GCC problem

Some versions of MSYS GCC include support for generating JSON
intermediate output format but incorrectly encode backslashes as \n:

  $ gcov -i example.gcda -t
  {
    "gcc_version": "9.2.0",
    [...]
    "current_working_directory": "C:\nTemp\nlcov\nexample",
    "data_file": "example.gcda"
  }

This causes geninfo to abort when trying to collect coverage data:

  Processing example.gcda
  geninfo: Unsuccessful open on filename containing newline at bin/geninfo line 2905.
  geninfo: WARNING: could not open C:
  Temp
  lcov
  example/example.c

Fix this by converting newlines in filenames on MSYS to /.

Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reported-by: fang.g@bigforce.cn

Author: oberpar

bin/geninfo

@@ -2160,6 +2160,12 @@ sub read_intermediate_json($$$)
 
 	$$basedir_ref = $json->{"current_working_directory"};
 
+	# Workaround for bug in MSYS GCC 9.x that encodes \ as \n in gcov JSON
+	# output
+	if ($^O eq "msys" && $$basedir_ref =~ /\n/) {
+		$$basedir_ref =~ s#\n#/#g;
+	}
+
 	for my $file (@{$json->{"files"}}) {
 		my $filename = $file->{"file"};