build: add some build options to customise library functionality

core/mt19937.c

@@ -217,6 +217,7 @@ static uint64_t genrand64_int64(struct fx_random_ctx *context)
 #endif
 }
 
+#if FX_ENABLE_FLOATING_POINT == 1
 /* generates a random number on [0,1]-real-interval */
 double genrand64_real1(struct fx_random_ctx *context)
 {
@@ -235,6 +236,7 @@ double genrand64_real3(struct fx_random_ctx *context)
 	return ((genrand64_int64(context) >> 12) + 0.5)
 	     * (1.0 / 4503599627370496.0);
 }
+#endif
 
 struct fx_random_algorithm z__fx_gen_mt19937 = {
 	.gen_name = "mt19937",