math: move i386 sqrtf to C with inline asm

src/math/i386/sqrtf.c

+#include <math.h>
+
+float sqrtf(float x)
+{
+	long double t;
+	/* The long double result has sufficient precision so that
+	 * second rounding to float still keeps the returned value
+	 * correctly rounded, see Pierre Roux, "Innocuous Double
+	 * Rounding of Basic Arithmetic Operations". */
+	__asm__ ("fsqrt" : "=t"(t) : "0"(x));
+	return (float)t;
+}

src/math/i386/sqrtf.s

-.global sqrtf
-.type sqrtf,@function
-sqrtf:	flds 4(%esp)
-	fsqrt
-	fstps 4(%esp)
-	flds 4(%esp)
-	ret