feat: Modularize RTS and extract headers/filesystem utilities

This commit restructures the Runtime System (RTS) components for better
modularity and reusability across different build configurations. The
changes enable cleaner separation of concerns and improved support for
cross-compilation scenarios.

Key changes:
- Extract RTS headers into standalone rts-headers package
  * Moved include/rts/Bytecodes.h to rts-headers
  * Moved include/rts/storage/ClosureTypes.h to rts-headers
  * Moved include/rts/storage/FunTypes.h to rts-headers
  * Moved include/stg/MachRegs/* to rts-headers
- Create rts-fs package for filesystem utilities
  * Extracted filesystem code from utils/fs
  * Provides reusable filesystem operations for RTS
- Rename utils/iserv to utils/ghc-iserv for consistency
  * Better naming alignment with other GHC utilities
  * Updated all references throughout the codebase
- Update RTS configuration and build files
  * Modified rts/configure.ac for new structure
  * Updated rts.cabal with new dependencies
  * Adjusted .gitignore for new artifacts

Rationale:
The modularization allows different stages of the compiler build to
share common RTS components without circular dependencies. This is
particularly important for:
- Cross-compilation where host and target RTS differ
- JavaScript backend which needs selective RTS components
- Stage1/Stage2 builds that require different RTS configurations

Contributors:
- Moritz Angermann: RTS modularization architecture and implementation
- Sylvain Henry: JavaScript backend RTS adjustments
- Andrea Bedini: Build system integration

This refactoring maintains full backward compatibility while providing
a cleaner foundation for multi-target support.

Author: Stable Haskell Team

compiler/GHC/Driver/Main.hs

@@ -1299,7 +1299,7 @@ hscDesugarAndSimplify summary (FrontendTypecheck tc_result) tc_warnings mb_old_h
           -- when compiling gHC_PRIM without generating code (e.g. with
           -- Haddock), we still want the virtual interface in the cache
           if ms_mod summary == gHC_PRIM
-            then return $ HscUpdate (getGhcPrimIface hsc_env)
+            then return $ HscUpdate (getGhcPrimIface (hsc_hooks hsc_env))
             else return $ HscUpdate iface
 
 
@@ -1314,7 +1314,7 @@ hscDesugarAndSimplify summary (FrontendTypecheck tc_result) tc_warnings mb_old_h
         -- when compiling gHC_PRIM without generating code (e.g. with
         -- Haddock), we still want the virtual interface in the cache
         if ms_mod summary == gHC_PRIM
-          then return $ HscUpdate (getGhcPrimIface hsc_env)
+          then return $ HscUpdate (getGhcPrimIface (hsc_hooks hsc_env))
           else return $ HscUpdate iface
 
 {-

compiler/GHC/Driver/Pipeline.hs

@@ -44,11 +44,14 @@ module GHC.Driver.Pipeline (
 
 
 import GHC.Prelude
+import GHC.Builtin.Names
 
 import GHC.Platform
 
 import GHC.Utils.Monad ( MonadIO(liftIO), mapMaybeM )
 
+import GHC.Builtin.Names
+
 import GHC.Driver.Main
 import GHC.Driver.Env hiding ( Hsc )
 import GHC.Driver.Errors
@@ -91,6 +94,7 @@ import GHC.Data.StringBuffer   ( hPutStringBuffer )
 import GHC.Data.Maybe          ( expectJust )
 
 import GHC.Iface.Make          ( mkFullIface )
+import GHC.Iface.Load          ( getGhcPrimIface )
 import GHC.Runtime.Loader      ( initializePlugins )
 
 
@@ -819,7 +823,13 @@ hscGenBackendPipeline pipe_env hsc_env mod_sum result = do
         let !linkable = Linkable part_time (ms_mod mod_sum) (NE.singleton (DotO final_object ModuleObject))
         -- Add the object linkable to the potential bytecode linkable which was generated in HscBackend.
         return (mlinkable { homeMod_object = Just linkable })
-  return (miface, final_linkable)
+
+  -- when building ghc-internal with --make (e.g. with cabal-install), we want
+  -- the virtual interface for gHC_PRIM in the cache, not the empty one.
+  let miface_final
+        | ms_mod mod_sum == gHC_PRIM = getGhcPrimIface (hsc_hooks hsc_env)
+        | otherwise                  = miface
+  return (miface_final, final_linkable)
 
 asPipeline :: P m => Bool -> PipeEnv -> HscEnv -> Maybe ModLocation -> FilePath -> m (Maybe ObjFile)
 asPipeline use_cpp pipe_env hsc_env location input_fn =

compiler/GHC/Runtime/Heap/Layout.hs

@@ -438,8 +438,8 @@ cardTableSizeW platform elems =
 -----------------------------------------------------------------------------
 -- deriving the RTS closure type from an SMRep
 
-#include "ClosureTypes.h"
-#include "FunTypes.h"
+#include "rts/storage/ClosureTypes.h"
+#include "rts/storage/FunTypes.h"
 -- Defines CONSTR, CONSTR_1_0 etc
 
 -- | Derives the RTS closure type from an 'SMRep'

compiler/GHC/StgToCmm/Layout.hs

@@ -549,7 +549,7 @@ mkVirtConstrSizes profile field_reps
 -------------------------------------------------------------------------
 
 -- bring in ARG_P, ARG_N, etc.
-#include "FunTypes.h"
+#include "rts/storage/FunTypes.h"
 
 mkArgDescr :: Platform -> [Id] -> ArgDescr
 mkArgDescr platform args

compiler/GHC/StgToCmm/TagCheck.hs

@@ -12,7 +12,7 @@ module GHC.StgToCmm.TagCheck
   ( emitTagAssertion, emitArgTagCheck, checkArg, whenCheckTags,
     checkArgStatic, checkFunctionArgTags,checkConArgsStatic,checkConArgsDyn) where
 
-#include "ClosureTypes.h"
+#include "rts/storage/ClosureTypes.h"
 
 import GHC.Prelude
 

rts-fs/README

@@ -0,0 +1,2 @@
+This "fs" library, used by various ghc utilities is used to share some common
+I/O filesystem functions with different packages.