Fix sinh's sign handling

In the musl 1.2.1 update, I made a change to disable the new code in
sinh for handling directed rounding modes, but I only incompletely
disabled it. This led to `sinh(-inf)` computing `inf` instead of `-inf`,
detected in [wasi-libc-test]. This patch fixes it.

[wasi-libc-test]: https://github.com/CraneStation/wasi-libc-test/tree/master/libc-test

libc-top-half/musl/src/math/sinh.c

@@ -37,7 +37,7 @@ double sinh(double x)
 #ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes
 	t = __expo2(absx, 2*h);
 #else
-	t = __expo2(absx);
+	t = 2*h*__expo2(absx);
 #endif
 	return t;
 }

libc-top-half/musl/src/math/sinhf.c

@@ -29,7 +29,7 @@ float sinhf(float x)
 #ifdef __wasilibc_unmodified_upstream // Wasm doesn't have alternate rounding modes
 	t = __expo2f(absx, 2*h);
 #else
-	t = __expo2f(absx);
+	t = 2*h*__expo2f(absx);
 #endif
 	return t;
 }