AddressSpaceStream: Fix Fuchsia build.

Virtio gpu related code should not be included in Fuchsia
builds since it's not implemented for Fuchsia.

TEST=fx build (with `optimize = "none"` in args.gn)

Change-Id: Ibef09a6a6c7050d27097962b2d95b88ad72a8a86
diff --git a/system/OpenglSystemCommon/AddressSpaceStream.cpp b/system/OpenglSystemCommon/AddressSpaceStream.cpp
index 4f26da9..ba9f289 100644
--- a/system/OpenglSystemCommon/AddressSpaceStream.cpp
+++ b/system/OpenglSystemCommon/AddressSpaceStream.cpp
@@ -142,7 +142,7 @@
     return res;
 }
 
-#ifdef HOST_BUILD
+#if defined(HOST_BUILD) || defined(__Fuchsia__)
 AddressSpaceStream* createVirtioGpuAddressSpaceStream(size_t ignored_bufSize) {
     // Ignore incoming ignored_bufSize
     (void)ignored_bufSize;
@@ -259,7 +259,7 @@
 
     return res;
 }
-#endif
+#endif // HOST_BUILD || __Fuchsia__
 
 
 AddressSpaceStream::AddressSpaceStream(