Make STDEXEC::system_context respect BUILD_SHARED_LIBS.

Author: jehelset

CMakeLists.txt

@@ -483,7 +483,7 @@ if (STDEXEC_ENABLE_NUMA)
 endif()
 
 set(SYSTEM_CONTEXT_SOURCES src/system_context/system_context.cpp)
-add_library(system_context STATIC ${SYSTEM_CONTEXT_SOURCES})
+add_library(system_context ${SYSTEM_CONTEXT_SOURCES})
 target_compile_features(system_context PUBLIC cxx_std_20)
 set_target_properties(system_context PROPERTIES
     CXX_STANDARD 20