Remove -Wno-unknown-pragmas from fusl build

fusl/src/math/fma.c

 #include <fenv.h>
 #include "libm.h"
 
 #if LDBL_MANT_DIG==64 && LDBL_MAX_EXP==16384
 /* exact add, assumes exponent_x >= exponent_y */
 static void add(long double *hi, long double *lo, long double x, long double y)
 {
         long double r;
 
         r = x + y;
@@ skipping 61 matching lines @@
 
 static int getexp(long double x)
 {
         union ldshape u;
         u.f = x;
         return u.i.se & 0x7fff;
 }
 
 double fma(double x, double y, double z)
 {
-        #pragma STDC FENV_ACCESS ON
+        PRAGMA_STDC_FENV_ACCESS_ON
         long double hi, lo1, lo2, xy;
         int round, ez, exy;
 
         /* handle +-inf,nan */
         if (!isfinite(x) || !isfinite(y))
                 return x*y + z;
         if (!isfinite(z))
                 return z;
         /* handle +-0 */
         if (x == 0.0 || y == 0.0)
@@ skipping 358 matching lines @@
                 return ret;
         }
 
         adj = add_adjusted(r.lo, xy.lo);
         if (spread + ilogb(r.hi) > -1023)
                 return scalbn(r.hi + adj, spread);
         else
                 return add_and_denormalize(r.hi, adj, spread);
 }
 #endif