Features: Quote all compiler names when comparing with COMPILER_ID

In preparation of adding MSVC support we need to quote all compiler names,
as MSVC is also a CMake variable.

Tests/CompileFeatures/CMakeLists.txt

@@ -1,5 +1,5 @@
 
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.1)
 
 project(CompileFeatures)
 
@@ -31,7 +31,7 @@ foreach(feature ${cxx_features})
   run_test(${feature} CXX)
 endforeach()
 
-if (CMAKE_CXX_COMPILER_ID STREQUAL GNU
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
     AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.8)
   # The cxx_alignof feature happens to work (for *this* testcase) with
   # GNU 4.7, but it is first documented as available with GNU 4.8.
@@ -39,7 +39,7 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL GNU
     cxx_alignof
   )
 endif()
-if (CMAKE_CXX_COMPILER_ID STREQUAL GNU
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
     AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.9)
   # GNU prior to 4.9 does not set any preprocessor define to distinguish
   # c++1y from c++11, so CMake does not support c++1y features before GNU 4.9.

Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.0.0)
+cmake_minimum_required(VERSION 3.1.0)
 project(WriteCompilerDetectionHeader)
 
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
@@ -56,17 +56,17 @@ macro(set_defines target true_defs false_defs)
   )
 endmacro()
 
-if (CMAKE_CXX_COMPILER_ID STREQUAL GNU
-    OR CMAKE_CXX_COMPILER_ID STREQUAL Clang
-    OR CMAKE_CXX_COMPILER_ID STREQUAL AppleClang)
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
+    OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang"
+    OR CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
   # False for C++98 mode.
   list(APPEND false_defs EXPECTED_COMPILER_CXX_DELEGATING_CONSTRUCTORS)
   list(APPEND false_defs EXPECTED_COMPILER_CXX_VARIADIC_TEMPLATES)
 endif()
 
-if (CMAKE_C_COMPILER_ID STREQUAL GNU
-    OR CMAKE_C_COMPILER_ID STREQUAL Clang
-    OR CMAKE_C_COMPILER_ID STREQUAL AppleClang)
+if (CMAKE_C_COMPILER_ID STREQUAL "GNU"
+    OR CMAKE_C_COMPILER_ID STREQUAL "Clang"
+    OR CMAKE_C_COMPILER_ID STREQUAL "AppleClang")
   add_executable(C_undefined c_undefined.c)
   set_property(TARGET C_undefined PROPERTY CXX_STANDARD 90)
   target_compile_options(C_undefined PRIVATE -Werror=undef)