buildsys: Don't add -ltomcrypt to "pkg-config --libs" after fallback to nettle
buildsys: Don't add -ltomcrypt to "pkg-config --libs" after fallback to nettle

If we used nettle because libtomcrypt was unavailable (not because the
user explicitly asked for nettle), @EXTRA_PC_LIBS@ was incorrectly
getting set to "-ltomcrypt".  Fix the logic so this does not happen.

Signed-off-by: Kevin Cernekee <3105dbb3dd63fbb4f6371cfb04adc6726f76c56b@gmail.com>

mtmiller/stoken,mtmiller/stoken,cernekee/stoken,cernekee/stoken,cernekee/stoken,mtmiller/stoken,cernekee/stoken,mtmiller/stoken