[build] Suppress warning spam in cst_units.c

[56988->12403/69950 ~560 28.901s] CC arm64-asan/obj/third_party/flite/src/wavesynth/flite.cst_units.c.o
../../third_party/flite/src/wavesynth/cst_units.c:593:9: warning: cast to smaller integer type 'int' from 'const unsigned char *' [-Wpointer-to-int-cast]
    p = (int)unit_residual; /* I know the compiler will complain about this */
        ^~~~~~~~~~~~~~~~~~
1 warning generated.

Change-Id: I8d0668e6916c1459c99f26fef7c8caab278dd2f7
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/flite/+/387758
Reviewed-by: Petr Hosek <phosek@google.com>
1 file changed