tcg: Remove stray semi-colons from target-*/helper.h

During GEN_HELPER=1, these are actually stray top-level semi-colons
which are technically invalid ISO C, but GCC accepts as an extension.
If we added enough __extension__ markers that we could dare use
-Wpedantic, we'd see

  warning: ISO C does not allow extra ‘;’ outside of a function

This will become a hard error in the next patch, wherein those ; will
appear in the middle of a data structure.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>