Do not cache CMAKE_CXX_STANDARD

This avoid stale values in the cache from blocking updates (eg c++17->20)

Signed-off-by: Matt Liberty <[email protected]>

Author: maliberty

CMakeLists.txt

@@ -59,7 +59,7 @@ set(OPENROAD_HOME ${PROJECT_SOURCE_DIR})
 set(OPENROAD_SHARE ${CMAKE_INSTALL_PREFIX}/share/openroad)
 
 # Default c++ standard used unless otherwise specified in target_compile_features.
-set(CMAKE_CXX_STANDARD 20 CACHE STRING "the C++ standard to use for this project")
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 # Disable compiler specific extensions like gnu++11.
 set(CMAKE_CXX_EXTENSIONS OFF)