disable constexpr test when C++ version < 20

Author: wusatosi

tests/beman/inplace_vector/CMakeLists.txt

@@ -10,13 +10,17 @@ target_link_libraries(beman.inplace_vector.test PRIVATE beman.inplace_vector)
 
 add_test(NAME beman.inplace_vector.test COMMAND beman.inplace_vector.test)
 
-# constexpr test
-add_executable(beman.inplace_vector.constexpr_test constexpr.test.cpp)
-target_link_libraries(
-    beman.inplace_vector.constexpr_test
-    PRIVATE beman.inplace_vector
-)
-add_test(
-    NAME beman.inplace_vector.constexpr_test
-    COMMAND beman.inplace_vector.constexpr_test
-)
+if(CMAKE_CXX_STANDARD GREATER_EQUAL 20)
+    # constexpr test
+    add_executable(beman.inplace_vector.constexpr_test constexpr.test.cpp)
+    target_link_libraries(
+        beman.inplace_vector.constexpr_test
+        PRIVATE beman.inplace_vector
+    )
+    add_test(
+        NAME beman.inplace_vector.constexpr_test
+        COMMAND beman.inplace_vector.constexpr_test
+    )
+else()
+    message(WARNING "C++20 or later is not enabled, skipping constexpr test.")
+endif()