Disable warnings C4503 on MSVC for test code

C4503 is "decorated name length exceeded", triggered
by some heavily templated types.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 12d0b59..fa778c3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -243,8 +243,14 @@
     add_executable(UnitSPIRV ${TEST_SOURCES})
     default_compile_options(UnitSPIRV)
     if(UNIX)
-     target_compile_options(UnitSPIRV PRIVATE
-        -Wno-undef)
+      target_compile_options(UnitSPIRV PRIVATE -Wno-undef)
+    endif()
+    if(${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.
+      # Important to do since we have warnings-as-errors.
+      target_compile_options(UnitSPIRV PRIVATE /wd4503)
     endif()
     target_include_directories(UnitSPIRV PRIVATE
       ${CMAKE_CURRENT_SOURCE_DIR}