When the compiler creates or uses a PCH file, it displays the following kind of message:

test.c: creating precompiled header file test.pch

You can suppress this message by using the compiler command-line option --no_pch_messages.

A verbose mode is available using --pch_verbose. In verbose mode, the compiler displays a message for each PCH file that is considered but cannot be used, giving the reason why it cannot be used.