wasm-cross (partial): arch(wasm32) shared-triple + RtsStartup wasm call guard

Two of the fixes #181 (feat/wasm-cross-ghcup) carries but the stable-ghc-9.14 /
#188 base lacks, needed to build stage3-wasm32-unknown-wasi:

* cabal.project.stage3: replace the stale `if os(wasi) { package * shared:True }`
  (which alone leaves GHC's wasm link pipeline inconsistent — fails at the
  ghc-internal link with [GHC-74335]) with #181's `if arch(wasm32)` triple
  (shared + executable-dynamic + rts +dynamic).
* rts/RtsStartup.c: guard the promoteBootLibrariesToGlobal() *call site* with
  !defined(wasm32_HOST_ARCH) to match its definition (which is already
  wasm-excluded; it uses dladdr/dlopen). Without this the wasm rts fails to
  compile ("call to undeclared function 'promoteBootLibrariesToGlobal'").

NOTE: these are necessary but NOT sufficient. stage3-wasm still fails at the
ghc-internal shared-lib link ([GHC-74335] "-dynamic ignored when linking
binaries on WASM" -> mismatched interface profile tag) because the real fix is
in the GHC COMPILER, on #181 but not here:
  - 4d84ace "compiler: per-target settings drive GHC Dynamic / Profiled"
    (Platform/Settings/Settings.IO/Driver.Session: targetIsDynamic etc.)
  - 7396909 "rts+compiler: wasm32 cross-target patches"
    (esp. compiler/GHC/Linker/Dynamic.hs — the wasm dynamic-link handling)
Porting those is the #181 <-> stable-ghc-9.14 wasm integration, tracked
separately. (7396909 also rewrites compiler/Setup.hs + ghc-boot/Setup.hs,
which conflicts with the modern-pin VerbosityHandles restore here.)

Author: angerman

cabal.project.stage3

@@ -1,6 +1,26 @@
 -- Configuration common to all stages
 import: cabal.project.common
 
+-- WASM target libraries are built shared so end-user TH/GHCi works at
+-- runtime via dyld.mjs (miso, jsaddle, aeson, …): the wasm libs then ship
+-- .dyn_hi + .so. Scoped to `arch(wasm32)` so it applies ONLY when cabal
+-- builds against the wasm32 --with-compiler — the native build-compiler
+-- packages (happy-lib, alex, Setup.hs) and the JS target are unaffected.
+--
+-- IMPORTANT: must be shared + executable-dynamic + `rts +dynamic` *together*.
+-- A `package * { shared: True }` alone (no executable-dynamic / rts +dynamic)
+-- under `if os(wasi)` leaves GHC's link pipeline inconsistent and fails at the
+-- ghc-internal link step ("[GHC-74335] -dynamic is ignored when linking
+-- binaries on WASM" → "mismatched interface file profile tag wanted \"\" got
+-- \"dyn\""). The full dynamic-everywhere triple is what makes the wasm link
+-- pipeline accept it. (Verified: this is the variant #181 ships green.)
+if arch(wasm32)
+  package *
+    shared: True
+    executable-dynamic: True
+  constraints:
+    rts +dynamic
+
 -- Disable Hackage, we explicitly include the packages we need.
 active-repositories: :none
 
@@ -173,13 +193,8 @@ package *
 package libffi-clib
   ghc-options: -no-rts
 
--- WASM/WASI-specific overrides:
--- - shared: True is required for GHCi/TH via dyld.mjs
--- - +use-system-libffi is already set unconditionally on package rts above,
---   but we keep this block for clarity and future conditional changes.
-if os(wasi)
-  package *
-    shared: True
+-- WASM/WASI shared-library overrides live in the `if arch(wasm32)` block near
+-- the top of this file (shared + executable-dynamic + rts +dynamic, together).
 
 package ghc
   flags: +build-tool-depends +internal-interpreter

rts/RtsStartup.c

@@ -424,7 +424,12 @@ hs_init_ghc(int *argc, char **argv[], RtsConfig rts_config)
 
     init_ghc_hs_iface();
 
-#if !defined(mingw32_HOST_OS) && defined(RTLD_NOLOAD)
+/* Must match the definition's #if at line 108: wasm32 is excluded there
+ * (promoteBootLibrariesToGlobal uses dladdr/dlopen, unavailable on wasm),
+ * but wasm DOES define RTLD_NOLOAD, so without the wasm32 exclusion here the
+ * call fires against an undefined function ("call to undeclared function
+ * 'promoteBootLibrariesToGlobal'"). */
+#if !defined(mingw32_HOST_OS) && !defined(wasm32_HOST_ARCH) && defined(RTLD_NOLOAD)
     /* Promote boot libraries to RTLD_GLOBAL for dynamic code loading.
      * See Note [Promoting Boot Libraries to RTLD_GLOBAL] */
     promoteBootLibrariesToGlobal();