Build system: add include directories and dependencies for generators

In the case of generating a file like this:

    GENERATE[foo.S]=mkfoo.pl arg1 arg2

the 'mkfoo.pl' generator itself might need to include other files,
such as perl modules within our source tree.  We can reuse already
existing syntax for it, like this:

    INCLUDE[mkfoo.pl]=module/path

or:

    DEPEND[mkfoo.pl]=modules/mymodule.pm

This change implements the support for such constructs, and for the
DEPEND statement, for any value that indicates a perl module (.pm
file), it will automatically infer an INCLUDE statement for its
directory, just like it does for C header files, so you won't have do
write this:

    DEPEND[mkfoo.pl]=modules/mymodule.pm
    INCLUDE[mkfoo.pl]=modules

Reviewed-by: Emilia Käsper <emilia@openssl.org>

Configurations/descrip.mms.tmpl

diff --git a/Configurations/descrip.mms.tmpl b/Configurations/descrip.mms.tmpl
index 2e58b1a..416f0ed 100644
--- a/Configurations/descrip.mms.tmpl
+++ b/Configurations/descrip.mms.tmpl
@@ -441,12 +441,13 @@
   sub generatesrc {
       my %args = @_;
       my $generator = join(" ", @{$args{generator}});
-      my $deps = join(", -\n\t\t", @{$args{deps}});
+      my $generator_incs = join("", map { ' "-I'.$_.'"' } @{$args{generator_incs}});
+      my $deps = join(", -\n\t\t", @{$args{generator_deps}}, @{$args{deps}});
 
       if ($args{src} !~ /\.[sS]$/) {
           return <<"EOF";
 $args{src} : $args{generator}->[0] $deps
-	\$(PERL) $generator > \$@
+	\$(PERL)$generator_incs $generator > \$@
 EOF
       } else {
           die "No method to generate assembler source present.\n";