build: disable blaise-rtl from default reactor build

RTL Pascal sources (System.pas, Classes.pas, etc.) are compiled by
the Blaise compiler, not FPC. C sources are compiled separately via
GCC. Marking blaise-rtl as activeByDefault=false excludes it from
'pasbuild compile' and 'pasbuild test' reactor runs; it can still be
built explicitly with 'pasbuild compile -m blaise-rtl'.

Also adds a bootstrapExclude entry for System.pas so that if
blaise-rtl is compiled explicitly, the FPC bootstrap program does not
include System (FPC provides it implicitly).

project.xml

@@ -10,7 +10,7 @@
   </build>
 
   <modules>
-    <module>rtl</module>
+    <module activeByDefault="false">rtl</module>
     <module>compiler</module>
     <module>tools/migration-analyser</module>
   </modules>

rtl/project.xml

@@ -6,6 +6,10 @@
   <build>
     <packaging>library</packaging>
     <!-- mainSource not needed — PasBuild auto-generates bootstrap -->
+    <!-- System.pas is compiled by Blaise, not FPC; FPC already provides System implicitly -->
+    <bootstrapExclude>
+      <unit>System</unit>
+    </bootstrapExclude>
   </build>
 
   <test>