In some cases, the code is fine, but GCC isn't smart enough to

In some cases, the code is fine, but GCC isn't smart enough to
figure that out; this usually happens when one variable is only
initialized and used when a particular condition holds true, and
we know that condition will never change within a given invocation
of the function.  In this case, we simply initialize the variables
to placate the compiler, hopefully to a value which will cause a
crash if it is ever actually used.
* print.c (scm_iprin1): Initialize mw_pos.
* read.c (scm_lreadrecparen): Initialize tl2, ans2.
* throw.c (scm_ithrow): Initialize dynpair.
* unif.c (scm_uniform_vector_ref): Initialize cra.
* struct.c (init_struct): Initialize prot.
* mbstrings.c (scm_print_mb_symbol): Initialize mw_pos and inc.