Revert templates to old behavior.

While emitting a template instantiation only once is good for compile times
and binary sizes, it doesn't work with linkonce linkage as inlined function
bodies could be discarded. Since we don't want to inhibit inlining, templates
are reverted to the previous behavior, where an instantiation is emitted for
each module using it.

In the future, a custom inlining pass may allow us to switch back to
common/weak linkage and reenable smart template instance emission.

dmd/template.c

@@ -2873,7 +2873,10 @@ TemplateInstance::TemplateInstance(Loc loc, Identifier *ident)
     this->havetempdecl = 0;
     this->isnested = NULL;
     this->errors = 0;
+
+    // LDC
     this->tinst = NULL;
+    this->tmodule = NULL;
 }
 
 /*****************
@@ -2988,6 +2991,7 @@ void TemplateInstance::semantic(Scope *sc)
 	tmodule = tinst->tmodule;
     else
 	tmodule = sc->module;
+    //printf("%s in %s\n", toChars(), tmodule->toChars());
 
 #if LOG
     printf("\tdo semantic\n");

gen/llvmhelpers.cpp

@@ -1557,13 +1557,14 @@ void DtoOverloadedIntrinsicName(TemplateInstance* ti, TemplateDeclaration* td, s
 
 bool mustDefineSymbol(Dsymbol* s)
 {
-#if 0
+#if 1
     return s->getModule() == gIR->dmodule || DtoIsTemplateInstance(s) != NULL;
 #else
     Module* M = DtoIsTemplateInstance(s);
     // if it's a template instance, check the instantiating module
     // not the module that defines the template
     if (M) {
+	//Logger::println("TINST %s from %s cur %s", s->toPrettyChars(), M->toChars(), gIR->dmodule->toChars());
         return M == gIR->dmodule;
     }
     return s->getCompilationModule() == gIR->dmodule;
@@ -1574,7 +1575,7 @@ bool mustDefineSymbol(Dsymbol* s)
 
 bool needsTemplateLinkage(Dsymbol* s)
 {
-#if 0
+#if 1
     return DtoIsTemplateInstance(s) != NULL;
 #else
     Module* M = DtoIsTemplateInstance(s);