[lld][WebAssembly] Fix check for implicitly exported mutable globals

This change is designed to avoid exporting mutable globals in the case
when mutable globals are not available.  However, it was being applied
in all cases even when mutable globals was enabled.

Author: sbc100

lld/test/wasm/mutable-global-exports.s

@@ -73,6 +73,9 @@ _start:
 # CHECK-ALL-NEXT:      - Name:            __wasm_call_ctors
 # CHECK-ALL-NEXT:        Kind:            FUNCTION
 # CHECK-ALL-NEXT:        Index:           0
+# CHECK-ALL-NEXT:      - Name:            __stack_pointer
+# CHECK-ALL-NEXT:        Kind:            GLOBAL
+# CHECK-ALL-NEXT:        Index:           0
 # CHECK-ALL-NEXT:      - Name:            _start
 # CHECK-ALL-NEXT:        Kind:            FUNCTION
 # CHECK-ALL-NEXT:        Index:           1

lld/wasm/Writer.cpp

@@ -784,6 +784,9 @@ void Writer::calculateExports() {
   unsigned globalIndex =
       out.importSec->getNumImportedGlobals() + out.globalSec->numGlobals();
 
+  bool hasMutableGlobals =
+      out.targetFeaturesSec->features.count("mutable-globals") > 0;
+
   for (Symbol *sym : symtab->symbols()) {
     if (!sym->isExported())
       continue;
@@ -801,7 +804,8 @@ void Writer::calculateExports() {
       }
       export_ = {name, WASM_EXTERNAL_FUNCTION, f->getExportedFunctionIndex()};
     } else if (auto *g = dyn_cast<DefinedGlobal>(sym)) {
-      if (g->getGlobalType()->Mutable && !g->getFile() && !g->forceExport) {
+      if (!hasMutableGlobals && g->getGlobalType()->Mutable && !g->getFile() &&
+          !g->isExportedExplicit()) {
         // Avoid exporting mutable globals are linker synthesized (e.g.
         // __stack_pointer or __tls_base) unless they are explicitly exported
         // from the command line.