Build: Verify that we're compiling with C++14.

CMakeLists.txt

@@ -1768,6 +1768,7 @@ file(GLOB VULKAN_LIST
     ${VULKAN_DIR}/*.cpp
     ${VULKAN_DIR}/*.h
     ${VULKAN_DIR}/*.hpp
+    ${SOURCE_DIR}/System/Build.cpp
     ${SOURCE_DIR}/System/Build.hpp
     ${SOURCE_DIR}/System/CPUID.cpp
     ${SOURCE_DIR}/System/CPUID.hpp

src/Android.bp

@@ -571,6 +571,7 @@ cc_defaults {
     ],
 
     srcs: [
+        "System/Build.cpp",
         "System/CPUID.cpp",
         "System/Configurator.cpp",
         "System/Half.cpp",

src/System/BUILD.gn

@@ -36,6 +36,7 @@ swiftshader_source_set("System_headers") {
 
 swiftshader_source_set("System") {
   sources = [
+    "Build.cpp",
     "CPUID.cpp",
     "Configurator.cpp",
     "Debug.cpp",

src/System/Build.cpp

+// Copyright 2020 The SwiftShader Authors. All Rights Reserved.
+//
+// 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.
+
+#if defined(_MSVC_LANG)
+#	define CPP_VERSION _MSVC_LANG
+#elif defined(__cplusplus)
+// Note: This must come after checking for _MSVC_LANG.
+// See https://developercommunity.visualstudio.com/content/problem/139261/msvc-incorrectly-defines-cplusplus.html
+#	define CPP_VERSION __cplusplus
+#endif
+
+#if !defined(CPP_VERSION) || CPP_VERSION <= 1
+#	error "Unable to identify C++ language version"
+#endif
+
+// The template and dummy function below verifies the compiler is using at least
+// C++14. It will print an error message containing the actual C++ version if
+// the version is < 14.
+
+namespace {
+
+template<int version>
+class cpp
+{
+	static_assert(version >= 2014, "SwiftShader requires at least C++14");
+};
+
+void check_cpp_version()
+{
+	cpp<CPP_VERSION / 100>();
+	(void)&check_cpp_version;  // dummy reference to avoid unreferenced function warning.
+}
+
+}  // namespace