cmake: Reimplement SECP256K1_APPEND_CFLAGS using Bitcoin Core approach

cmake/AllTargetsCompileOptions.cmake

@@ -1,12 +0,0 @@
-# Add compile options to all targets added in the subdirectory.
-function(all_targets_compile_options dir options)
-  get_directory_property(targets DIRECTORY ${dir} BUILDSYSTEM_TARGETS)
-  separate_arguments(options)
-  set(compiled_target_types STATIC_LIBRARY SHARED_LIBRARY OBJECT_LIBRARY EXECUTABLE)
-  foreach(target ${targets})
-    get_target_property(type ${target} TYPE)
-    if(type IN_LIST compiled_target_types)
-      target_compile_options(${target} PRIVATE ${options})
-    endif()
-  endforeach()
-endfunction()