user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/options/ansi/musl-generic-math/trunc.c

@@ -0,0 +1,19 @@
+#include "libm.h"
+
+double trunc(double x)
+{
+	union {double f; uint64_t i;} u = {x};
+	int e = (int)(u.i >> 52 & 0x7ff) - 0x3ff + 12;
+	uint64_t m;
+
+	if (e >= 52 + 12)
+		return x;
+	if (e < 12)
+		e = 1;
+	m = -1ULL >> e;
+	if ((u.i & m) == 0)
+		return x;
+	FORCE_EVAL(x + 0x1p120f);
+	u.i &= ~m;
+	return u.f;
+}