Remove source/instruction.cpp

Avoids linker problems on Windows and OSX with duplicate object file
names.  Avoids collision with source/val/instruction.cpp

Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/451
diff --git a/source/CMakeLists.txt b/source/CMakeLists.txt
index 0324aea..4b9c52d 100644
--- a/source/CMakeLists.txt
+++ b/source/CMakeLists.txt
@@ -142,7 +142,6 @@
   ${CMAKE_CURRENT_SOURCE_DIR}/diagnostic.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/disassemble.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/ext_inst.cpp
-  ${CMAKE_CURRENT_SOURCE_DIR}/instruction.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/libspirv.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/message.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/name_mapper.cpp
diff --git a/source/instruction.cpp b/source/instruction.cpp
deleted file mode 100644
index 8436fdc..0000000
--- a/source/instruction.cpp
+++ /dev/null
@@ -1,20 +0,0 @@
-// Copyright (c) 2015-2016 The Khronos Group Inc.
-//
-// 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.
-
-#include "instruction.h"
-
-void spvInstructionAddWord(spv_instruction_t* inst, uint32_t value) {
-  inst->words.push_back(value);
-}
-
diff --git a/source/instruction.h b/source/instruction.h
index ff735e7..5dd4d13 100644
--- a/source/instruction.h
+++ b/source/instruction.h
@@ -42,6 +42,8 @@
 };
 
 // Appends a word to an instruction, without checking for overflow.
-void spvInstructionAddWord(spv_instruction_t* inst, uint32_t value);
+inline void spvInstructionAddWord(spv_instruction_t* inst, uint32_t value) {
+  inst->words.push_back(value);
+}
 
 #endif  // LIBSPIRV_INSTRUCTION_H_