nit: remove compiler warnings

nit: remove compiler warnings

"log_error(LOG_LEVEL_FATAL, ..." doesn't return but apparently the compiler doesn't know that.
Get rid of several "this statement may fall through [-Wimplicit-fallthrough=]" warnings.

i686-w64-mingw32-gcc -c -Imbedtls/include -pipe -O2 -fstack-protector-strong -D_FORTIFY_SOURCE=2 -Wall -Wextra -Wno-missing-field-initializers -Wno-sign-compare -Wno-type-limits -Wno-unused-parameter -Wno-unused-but-set-variable -Wformat=2 -Wlogical-op -Wshadow -DNDEBUG -DWINVER=0x501  -I/source/pcre-8.44/ -I/source/mbedtls-2.16.10/include -I/source/brotli-1.0.9/c/include  -mwindows -Wall  jcc.c -o jcc.o
jcc.c: In function ‘bind_port_helper’:
jcc.c:5820:13: warning: this statement may fall through [-Wimplicit-fallthrough=]
 5820 |             log_error(LOG_LEVEL_FATAL,
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~
 5821 |                "can't bind to %s:%d: There may be another Privoxy "
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 5822 |                "or some other proxy running on port %d",
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 5823 |                bind_address, hport, hport);
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~
jcc.c:5825:10: note: here
 5825 |          case -2:
      |          ^~~~