Warn that SUPPORT_BIG_ENDIAN is experimental (#25058)

Support for big endian targets is "best effort" and not fully supported
or tested.

Also, as far as I'm aware there is only one or two users of this feature
so I think it makes sense for it to stay as "best effort" for the
foreseeable future.

See #25042

Author: sbc100

site/source/docs/tools_reference/settings_reference.rst

@@ -427,6 +427,8 @@ function call that uses DataView to enforce LE byte order for HEAP buffer;
 This makes generated JavaScript run on BE as well as LE machines. (If 0, only
 LE systems are supported). Does not affect generated wasm.
 
+.. note:: This is an experimental setting
+
 Default value: false
 
 .. _safe_heap:

src/settings.js

@@ -317,6 +317,7 @@ var INLINING_LIMIT = false;
 // function call that uses DataView to enforce LE byte order for HEAP buffer;
 // This makes generated JavaScript run on BE as well as LE machines. (If 0, only
 // LE systems are supported). Does not affect generated wasm.
+// [experimental]
 var SUPPORT_BIG_ENDIAN = false;
 
 // Check each write to the heap, for example, this will give a clear

tools/link.py

@@ -840,6 +840,9 @@ def phase_linker_setup(options, linker_args):  # noqa: C901, PLR0912, PLR0915
   if settings.GROWABLE_ARRAYBUFFERS:
     diagnostics.warning('experimental', '-sGROWABLE_ARRAYBUFFERS is still experimental and not yet supported in browsers')
 
+  if settings.SUPPORT_BIG_ENDIAN:
+    diagnostics.warning('experimental', '-sSUPPORT_BIG_ENDIAN is experimental, not all features are fully supported.')
+
   if settings.WASM_ESM_INTEGRATION:
     diagnostics.warning('experimental', '-sWASM_ESM_INTEGRATION is still experimental and not yet supported in browsers')
     default_setting('MODULARIZE', 'instance')