Add Compiler.flavor

f253d68b85 added support
for #RAKUDO_FLAVOR# in source code that is being handled by the
tools/build/gen-cat.nqp script.

This commit slightly tweaks that, by just returning the actual
string found in %*ENV<RAKUDO_FLAVOR> without a space prefixed.
Adapt Compiler.nqp accordingly and add method "flavor" so that
any code can introspect which flavor of Rakudo is being run.

This could e.g. be used to assume (non-)availability of installed
modules depending on the flavor, or just simply add the flavor to
certain (error) messages.

src/Perl6/Compiler.nqp

@@ -165,10 +165,12 @@ class Perl6::Compiler is HLL::Compiler {
             $raku   := "Raku®";
             $rakudo := "Rakudo™";
         }
+        my $flavor := #RAKUDO_FLAVOR#;
+        $flavor := " $flavor" if $flavor;
 
         "Welcome to "
           ~ $rakudo
-          ~ #RAKUDO_FLAVOR#
+          ~ $flavor
           ~ " v"
           ~ $config-version
           ~ ".\nImplementing the "

src/core.c/Compiler.rakumod

@@ -27,6 +27,7 @@ class Compiler does Systemic {
     }
 
     method backend() { $name }
+    method flavor()  { #RAKUDO_FLAVOR# }
 
     proto method id(|) {*}
     multi method id(Compiler:U:) { $compilation-id }

tools/build/gen-cat.nqp

@@ -59,7 +59,6 @@ sub MAIN(*@ARGS) {
                   nqp::atkey(nqp::getenvhash, 'RAKUDO_FLAVOR'),
                   ""
                 );
-                $flavor := " $flavor" if $flavor;
                 print(
                   nqp::join("'$flavor'", nqp::split('#RAKUDO_FLAVOR#', $_))
                 );