Use NEW behavior for policy CMP0054.

The NEW behavior is to not dereference variables or interpret keywords
that have been quoted or bracketed.

For more information, see
https://cmake.org/cmake/help/v3.1/policy/CMP0054.html.

This is to suppress a warning when using CMake 3.1.3+.
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 1ac7a6b..7286eda 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -51,7 +51,7 @@
     if(${COMPILER_IS_LIKE_GNU})
       target_compile_options(${ARG_TARGET} PRIVATE -Wno-undef)
     endif()
-    if(${CMAKE_CXX_COMPILER_ID} STREQUAL "MSVC")
+    if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
       # Disable C4503 "decorated name length exceeded" warning,
       # triggered by some heavily templated types.
       # We don't care much about that in test code.