Fix MSVC identification for modules support

Can't use `MSVC` var because it is also true for clang-cl. Fixes #500.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index fbd223e..a1d49c4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,7 +42,7 @@
 add_library(Vulkan::Headers ALIAS Vulkan-Headers)
 target_include_directories(Vulkan-Headers INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>)
 
-if (MSVC AND (MSVC_VERSION GREATER_EQUAL "1941") OR
+if ((CMAKE_CXX_COMPILER_ID STREQUAL "MSVC" AND (MSVC_VERSION GREATER_EQUAL "1941")) OR
     # clang-cl doesn't currently support modules
     (CMAKE_CXX_COMPILER_ID STREQUAL "Clang"
         AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "16.0"