msvcrt: Use the __rem_pio2()/__rem_pio2f() implementation from the bundled musl library.

libs/musl/src/math/__rem_pio2.c

@@ -119,7 +119,7 @@ int __rem_pio2(double x, double *y)
 	if (ix < 0x413921fb) {  /* |x| ~< 2^20*(pi/2), medium size */
 medium:
 		/* rint(x/(pi/2)) */
-		fn = (double_t)x*invpio2 + toint - toint;
+		fn = rint(x * invpio2);
 		n = (int32_t)fn;
 		r = x - fn*pio2_1;
 		w = fn*pio2_1t;  /* 1st round, good to 85 bits */

libs/musl/src/math/__rem_pio2f.c

@@ -52,7 +52,7 @@ int __rem_pio2f(float x, double *y)
 	/* 25+53 bit pi is good enough for medium size */
 	if (ix < 0x4dc90fdb) {  /* |x| ~< 2^28*(pi/2), medium size */
 		/* Use a specialized rint() to get fn. */
-		fn = (double_t)x*invpio2 + toint - toint;
+		fn = fp_barrier(x * invpio2 + toint) - toint;
 		n  = (int32_t)fn;
 		*y = x - fn*pio2_1 - fn*pio2_1t;
 		/* Matters with directed rounding. */