Remove -Wno-unknown-pragmas from fusl build

fusl/src/math/nearbyint.c

 #include <fenv.h>
 #include <math.h>
+#include "libm.h"
 
 /* nearbyint is the same as rint, but it must not raise the inexact exception */
 
 double nearbyint(double x)
 {
 #ifdef FE_INEXACT
-        #pragma STDC FENV_ACCESS ON
+        PRAGMA_STDC_FENV_ACCESS_ON
         int e;
 
         e = fetestexcept(FE_INEXACT);
 #endif
         x = rint(x);
 #ifdef FE_INEXACT
         if (!e)
                 feclearexcept(FE_INEXACT);
 #endif
         return x;
 }