Add a basic linker script

Ensures that the multiboot header is early in the executable.

src/arch/x86_64/linker.ld

@@ -0,0 +1,32 @@
+/*
+Copyright 2015 Philipp Oppermann
+
+Licensed under the Apache License, Version 2.0 (the "License")
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+ENTRY(start)
+
+SECTIONS {
+  . = 1M;
+
+  .boot :
+  {
+    /* ensure that the multiboot header is at the beginning */
+    *(.multiboot)
+  }
+
+  .text :
+  {
+    *(.text)
+  }
+}