d: Fix ICE in finish_thunk (PR97644)

Because this what the upstream reference compiler did, thunks for the D
front-end were associated with the class definition, so were forced
code-gen even if the target function was extern.  This has now been
changed so there are now only generated if there is a function
definition, fixing the ICE that occurred in PR 97644, which was caused
by calling expand_thunk() early.

gcc/d/ChangeLog:

	PR d/97644
	* dmd/MERGE: Merge upstream dmd 95044d8e4.
	* d-target.cc (TargetCPP::thunkMangle): New function.
	* decl.cc (finish_thunk): Don't force expand thunks for external
	functions.
	(make_thunk): Emit thunks only if the function has a definition.
	Generate correct mangling for thunks to C++ classes.

gcc/testsuite/ChangeLog:

	* gdc.dg/pr92216.d: Update scan-assember.

1 files changed, 19 insertions, 1 deletions

diff --git a/gcc/d/dmd/cppmangle.c b/gcc/d/dmd/cppmangle.c
index b361d37..3f571fc 100644
--- a/gcc/d/dmd/cppmangle.c
+++ b/gcc/d/dmd/cppmangle.c
@@ -582,13 +582,21 @@ class CppMangleVisitor : public Visitor
         //printf("mangle_function(%s)\n", d->toChars());
         /*
          * <mangled-name> ::= _Z <encoding>
+         */
+        buf->writestring("_Z");
+        this->mangle_function_encoding(d);
+    }
+
+    void mangle_function_encoding(FuncDeclaration *d)
+    {
+        //printf("mangle_function_encoding(%s)\n", d->toChars());
+        /*
          * <encoding> ::= <function name> <bare-function-type>
          *            ::= <data name>
          *            ::= <special-name>
          */
         TypeFunction *tf = (TypeFunction *)d->type;
 
-        buf->writestring("_Z");
         if (getFuncTemplateDecl(d))
         {
             /* It's an instance of a function template
@@ -1132,3 +1140,13 @@ const char *cppTypeInfoMangleItanium(Dsymbol *s)
     v.cpp_mangle_name(s, false);
     return buf.extractChars();
 }
+
+const char *cppThunkMangleItanium(FuncDeclaration *fd, int offset)
+{
+    //printf("cppThunkMangleItanium(%s)\n", fd.toChars());
+    OutBuffer buf;
+    buf.printf("_ZThn%u_", offset);  // "Th" means thunk, "n%u" is the call offset
+    CppMangleVisitor v(&buf, fd->loc);
+    v.mangle_function_encoding(fd);
+    return buf.extractChars();
+}