Unified - Add the build.info command OVERRIDE, to avoid build file clashes

Should it be needed because the recipes within a RAW section might
clash with those generated by Configure, it's possible to tell it
not to generate them with the use of OVERRIDES, for example:

    SOURCE[libfoo]=foo.c bar.c

    OVERRIDES=bar.o
    BEGINRAW[Makefile(unix)]
    bar.o: bar.c
        $(CC) $(CFLAGS) -DSPECIAL -c -o $@ $<
    ENDRAW[Makefile(unix)]
Reviewed-by: NRich Salz <rsalz@openssl.org>

Configurations/README

@@ -404,6 +404,18 @@ configuration items:
    build hoho.h: echo "/* hoho */" > hoho.h
    ENDRAW[build.ninja(unix)]
 
+Should it be needed because the recipes within a RAW section might
+clash with those generated by Configure, it's possible to tell it
+not to generate them with the use of OVERRIDES, for example:
+
+    SOURCE[libfoo]=foo.c bar.c
+    
+    OVERRIDES=bar.o
+    BEGINRAW[Makefile(unix)]
+    bar.o: bar.c
+    	$(CC) $(CFLAGS) -DSPECIAL -c -o $@ $<
+    ENDRAW[Makefile(unix)]
+
 See the documentation further up for more information on configuration
 items.
 

Configurations/common.tmpl

@@ -134,6 +134,9 @@
      $cache{$script} = 1;
  }
 
+ # Start with populating the cache with all the overrides
+ %cache = map { $_ => 1 } @{$unified_info{overrides}};
+
  # Build all known libraries, engines, programs and scripts.
  # Everything else will be handled as a consequence.
  map { dolib($_) } @{$unified_info{libraries}};

Configure

@@ -1274,6 +1274,7 @@ if ($builder eq "unified") {
         my @engines = ();
         my @scripts = ();
         my @extra = ();
+        my @overrides = ();
         my @intermediates = ();
         my @rawlines = ();
 
@@ -1342,6 +1343,9 @@ if ($builder eq "unified") {
             qr/^\s*EXTRA\s*=\s*(.*)\s*$/
             => sub { push @extra, split(/\s+/, $1)
                          if !@skip || $skip[$#skip] > 0 },
+            qr/^\s*OVERRIDES\s*=\s*(.*)\s*$/
+            => sub { push @overrides, split(/\s+/, $1)
+                         if !@skip || $skip[$#skip] > 0 },
 
             qr/^\s*ORDINALS\[((?:\\.|[^\\\]])+)\]\s*=\s*(.*)\s*$/,
             => sub { push @{$ordinals{$1}}, split(/\s+/, $2)
@@ -1440,6 +1444,11 @@ EOF
             $unified_info{extra}->{$extra} = 1;
         }
 
+        foreach (@overrides) {
+            my $override = cleanfile($buildd, $_, $blddir);
+            $unified_info{overrides}->{$override} = 1;
+        }
+
         push @{$unified_info{rawlines}}, @rawlines;
 
         unless ($disabled{shared}) {
@@ -1583,7 +1592,7 @@ EOF
 
     ### Make unified_info a bit more efficient
     # One level structures
-    foreach (("programs", "libraries", "engines", "scripts", "extra")) {
+    foreach (("programs", "libraries", "engines", "scripts", "extra", "overrides")) {
         $unified_info{$_} = [ sort keys %{$unified_info{$_}} ];
     }
     # Two level structures