[analyzer] Fix scan-build to handle missing output directories.

[ygribov]

Summary

Cwd::abs_path has a somewhat tricky semantics: if it's operand directory does not exist, it'll return undefined (see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=257568). This may cause scan-build to silently ignore output directory (specified with -o) and use /tmp instead of trying to create directory. This tiny patch fixes the problem.

[dcoughlin]

Looks good to me. I will commit.

tools/scan-build/scan-build

if ($arg eq "-o") {
       shift @$Args;
 
       if (!@$Args) {
         DieDiag("'-o' option requires a target directory name.\n");
       }
 
       # Construct an absolute path.  Uses the current working directory
       # as a base if the original path was not absolute.
-      $Options{OutputDir} = abs_path(shift @$Args);
+      my $OutDir = shift @$Args;
+      mkpath($OutDir) unless (-e $OutDir);  # abs_path wants existing dir
+      $Options{OutputDir} = abs_path($OutDir);
 
       next;
     }
 
     if ($arg =~ /^--html-title(=(.+))?$/) {
       shift @$Args;
 
       if (!defined $2 || $2 eq '') {