Fix issue #3795 - Fix LDC linked dynamically

with Phobos and DRuntime when built with GDMD.

Prepend each argument in D_LINKER_ARGS with "-Wl," when using GDMD.
The above is needed because the arguments reported by GDMD are what is
passed to COLLECT2 while D_LINKER_ARGS are later passed to CXX.
The problem with that is that without "-Wl," prefix the -Bstatic and
-Bdynamic arguments before and after -lgphobos and -libgdruntime are
dropped. And that is a problem because without these the produced LDC is
linked dynamically to libgphobos and libgdruntime so these have to be
available whereever LDC is used.

Once libgphobos and libgdruntime were linked statically several symbol
conflicts were revealed which are fixed by moving the offending symbols
within "version (LDC)" blocks.

cmake/Modules/ExtractDMDSystemLinker.cmake

@@ -69,7 +69,7 @@ if("${D_COMPILER_ID}" STREQUAL "GDMD")
     set(D_LINKER_ARGS)
     foreach(arg ${linker_line})
         if("${arg}" MATCHES ^-L.*|^-l.*|^-B.*)
-            list(APPEND D_LINKER_ARGS "${arg}")
+            list(APPEND D_LINKER_ARGS "-Wl,${arg}")
         endif()
     endforeach()
 else()

dmd/root/rmem.d

@@ -220,9 +220,12 @@ static if (OVERRIDE_MEMALLOC)
     // That scheme is faster and comes with less memory overhead than using a
     // disabled GC alone.
 
-    extern (C) void* _d_allocmemory(size_t m_size) nothrow
+    version (LDC)
     {
-        return allocmemory(m_size);
+        extern (C) void* _d_allocmemory(size_t m_size) nothrow
+        {
+            return allocmemory(m_size);
+        }
     }
 
     private void* allocClass(const ClassInfo ci) nothrow pure
@@ -242,13 +245,16 @@ static if (OVERRIDE_MEMALLOC)
 
     extern (C) void* _d_newitemU(const TypeInfo ti) nothrow;
 
-    extern (C) Object _d_newclass(const ClassInfo ci) nothrow
+    version (LDC)
     {
-        const initializer = ci.initializer;
+        extern (C) Object _d_newclass(const ClassInfo ci) nothrow
+        {
+            const initializer = ci.initializer;
 
-        auto p = mem.isGCEnabled ? allocClass(ci) : allocmemoryNoFree(initializer.length);
-        memcpy(p, initializer.ptr, initializer.length);
-        return cast(Object) p;
+            auto p = mem.isGCEnabled ? allocClass(ci) : allocmemoryNoFree(initializer.length);
+            memcpy(p, initializer.ptr, initializer.length);
+            return cast(Object) p;
+        }
     }
 
     version (LDC)
@@ -262,19 +268,25 @@ static if (OVERRIDE_MEMALLOC)
         }
     }
 
-    extern (C) void* _d_newitemT(TypeInfo ti) nothrow
+    version (LDC)
     {
-        auto p = mem.isGCEnabled ? _d_newitemU(ti) : allocmemoryNoFree(ti.tsize);
-        memset(p, 0, ti.tsize);
-        return p;
+        extern (C) void* _d_newitemT(TypeInfo ti) nothrow
+        {
+            auto p = mem.isGCEnabled ? _d_newitemU(ti) : allocmemoryNoFree(ti.tsize);
+            memset(p, 0, ti.tsize);
+            return p;
+        }
     }
 
-    extern (C) void* _d_newitemiT(TypeInfo ti) nothrow
+    version (LDC)
     {
-        auto p = mem.isGCEnabled ? _d_newitemU(ti) : allocmemoryNoFree(ti.tsize);
-        const initializer = ti.initializer;
-        memcpy(p, initializer.ptr, initializer.length);
-        return p;
+        extern (C) void* _d_newitemiT(TypeInfo ti) nothrow
+        {
+            auto p = mem.isGCEnabled ? _d_newitemU(ti) : allocmemoryNoFree(ti.tsize);
+            const initializer = ti.initializer;
+            memcpy(p, initializer.ptr, initializer.length);
+            return p;
+        }
     }
 
     // TypeInfo.initializer for compilers older than 2.070