filter-showIncludes: filter out system headers

A blacklist based approach doesn't seem easy since there are various
different SDKs, MFC, ATL and whatnot each potentially with an own
include path; so simply whitelist the known source and build dirs.

Change-Id: I93b27bd0ffbd57237da2d23afa95dea7c0785774

solenv/gbuild/filter-showIncludes.pl

@@ -43,6 +43,11 @@ while ( <STDIN> ) {
         chomp;
         s/\\/\//g;
 
+
+        # skip system headers, i.e. everything not under source or build dirs
+        if ( /$ENV{'SRCDIR'}|$ENV{'OUTDIR'}|$ENV{'WORKDIR'}/ )
+        {
+
         # X: -> /cygdrive/x/
         s/^(.):/\/cygdrive\/\l\1/;
 
@@ -52,6 +57,7 @@ while ( <STDIN> ) {
             $seen{$_} = 1;
             print $OUT " \\\n  $_";
         }
+        }
     }
     else {
         # skip the first line, it always just duplicates what is being