math: use float_t and double_t in scalbnf and scalbn

remove STRICT_ASSIGN (c99 semantics is assumed) and use the conventional
union to prepare the scaling factor (so libm.h is no longer needed)

src/math/scalbn.c

-#include "libm.h"
+#include <math.h>
+#include <stdint.h>
 
 double scalbn(double x, int n)
 {
-	double scale;
+	union {double f; uint64_t i;} u;
+	double_t y = x;
 
 	if (n > 1023) {
-		x *= 0x1p1023;
+		y *= 0x1p1023;
 		n -= 1023;
 		if (n > 1023) {
-			x *= 0x1p1023;
+			y *= 0x1p1023;
 			n -= 1023;
 			if (n > 1023)
 				n = 1023;
 		}
 	} else if (n < -1022) {
-		x *= 0x1p-1022;
+		y *= 0x1p-1022;
 		n += 1022;
 		if (n < -1022) {
-			x *= 0x1p-1022;
+			y *= 0x1p-1022;
 			n += 1022;
 			if (n < -1022)
 				n = -1022;
 		}
 	}
-	INSERT_WORDS(scale, (uint32_t)(0x3ff+n)<<20, 0);
-	STRICT_ASSIGN(double, x, x * scale);
+	u.i = (uint64_t)(0x3ff+n)<<52;
+	x = y * u.f;
 	return x;
 }

src/math/scalbnf.c

-#include "libm.h"
+#include <math.h>
+#include <stdint.h>
 
 float scalbnf(float x, int n)
 {
-	float scale;
+	union {float f; uint32_t i;} u;
+	float_t y = x;
 
 	if (n > 127) {
-		x *= 0x1p127f;
+		y *= 0x1p127f;
 		n -= 127;
 		if (n > 127) {
-			x *= 0x1p127f;
+			y *= 0x1p127f;
 			n -= 127;
 			if (n > 127)
 				n = 127;
 		}
 	} else if (n < -126) {
-		x *= 0x1p-126f;
+		y *= 0x1p-126f;
 		n += 126;
 		if (n < -126) {
-			x *= 0x1p-126f;
+			y *= 0x1p-126f;
 			n += 126;
 			if (n < -126)
 				n = -126;
 		}
 	}
-	SET_FLOAT_WORD(scale, (uint32_t)(0x7f+n)<<23);
-	STRICT_ASSIGN(float, x, x * scale);
+	u.i = (uint32_t)(0x7f+n)<<23;
+	x = y * u.f;
 	return x;
 }