$ cc -O2 -Wall -o fixpt_harness fixpt_harness.c
fixpt_harness.c:57:18: warning: 'div64_s64' defined but not used [-Wunused-function]
 static long long div64_s64(long long n, long long d) { return n / d; }
                  ^~~~~~~~~
fixpt_harness.c:46:32: warning: 'dc_fixpt_two_pi' defined but not used [-Wunused-const-variable=]
 static const struct fixed31_32 dc_fixpt_two_pi = { 26986075409LL };
                                ^~~~~~~~~~~~~~~
fixpt_harness.c:43:32: warning: 'dc_fixpt_zero' defined but not used [-Wunused-const-variable=]
 static const struct fixed31_32 dc_fixpt_zero = { 0 };
                                ^~~~~~~~~~~~~~
(warnings are expected: verbatim library code keeps unused siblings)
BUILD_EXIT=0