math: move x87-family rint functions to C with inline asm

src/math/i386/rint.c

+#include <math.h>
+
+double rint(double x)
+{
+	__asm__ ("frndint" : "+t"(x));
+	return x;
+}

src/math/i386/rint.s

-.global rint
-.type rint,@function
-rint:
-	fldl 4(%esp)
-	frndint
-	ret

src/math/i386/rintf.c

+#include <math.h>
+
+float rintf(float x)
+{
+	__asm__ ("frndint" : "+t"(x));
+	return x;
+}

src/math/i386/rintf.s

-.global rintf
-.type rintf,@function
-rintf:
-	flds 4(%esp)
-	frndint
-	ret

src/math/i386/rintl.c

+#include <math.h>
+
+long double rintl(long double x)
+{
+	__asm__ ("frndint" : "+t"(x));
+	return x;
+}

src/math/i386/rintl.s

-.global rintl
-.type rintl,@function
-rintl:
-	fldt 4(%esp)
-	frndint
-	ret

src/math/x86_64/rintl.c

+#include <math.h>
+
+long double rintl(long double x)
+{
+	__asm__ ("frndint" : "+t"(x));
+	return x;
+}

src/math/x86_64/rintl.s

-.global rintl
-.type rintl,@function
-rintl:
-	fldt 8(%rsp)
-	frndint
-	ret