[C++20] [Modules] Treat in class defined member functions in language linkage as implicitly inline

Close llvm#108732

This looks liek an oversight mostly.

(cherry picked from commit 7046a9f)

Author: ChuanqiXu9

clang/lib/Sema/SemaDecl.cpp

@@ -9734,7 +9734,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     bool ImplicitInlineCXX20 = !getLangOpts().CPlusPlusModules ||
                                NewFD->isConstexpr() || NewFD->isConsteval() ||
                                !NewFD->getOwningModule() ||
-                               NewFD->isFromExplicitGlobalModule() ||
+                               NewFD->isFromGlobalModule() ||
                                NewFD->getOwningModule()->isHeaderLikeModule();
     bool isInline = D.getDeclSpec().isInlineSpecified();
     bool isVirtual = D.getDeclSpec().isVirtualSpecified();

clang/test/Modules/pr108732.cppm

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -std=c++20 %s -ast-dump | FileCheck %s
+export module mod;
+
+extern "C++" {
+class C
+{
+public:
+bool foo() const {
+    return true;
+}
+};
+}
+
+// CHECK: foo {{.*}}implicit-inline