Remove -Wno-unknown-pragmas from fusl build

fusl/src/math/nearbyintl.c

 #include <math.h>
 #include <float.h>
+#include "libm.h"
 
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
 long double nearbyintl(long double x)
 {
         return nearbyint(x);
 }
 #else
 #include <fenv.h>
 long double nearbyintl(long double x)
 {
 #ifdef FE_INEXACT
-        #pragma STDC FENV_ACCESS ON
+        PRAGMA_STDC_FENV_ACCESS_ON
         int e;
 
         e = fetestexcept(FE_INEXACT);
 #endif
         x = rintl(x);
 #ifdef FE_INEXACT
         if (!e)
                 feclearexcept(FE_INEXACT);
 #endif
         return x;
 }
 #endif