updated occurrences of PI_2 with PI_OVER_2, to match existing declaration

Author: wldfngrs

libc/src/math/generic/acosf16.cpp

@@ -80,15 +80,15 @@ LLVM_LIBC_FUNCTION(float16, acosf16, (float16 x)) {
   if (x_abs <= 0x3800) {
     // if x is 0, return pi/2
     if (LIBC_UNLIKELY(x_abs == 0))
-      return fputil::cast<float16>(PI_2);
+      return fputil::cast<float16>(PI_OVER_2);
 
     // Note that: acos(x) = pi/2 + asin(-x) = pi/2 - asin(x)
     // Degree-6 minimax polynomial of asin(x) generated by Sollya with:
     // > P = fpminimax(asin(x)/x, [|0, 2, 4, 6, 8|], [|SG...|], [0, 0.5]);
     float interm =
         fputil::polyeval(xsq, 0x1.000002p0f, 0x1.554c2ap-3f, 0x1.3541ccp-4f,
                          0x1.43b2d6p-5f, 0x1.a0d73ep-5f);
-    return fputil::cast<float16>(fputil::multiply_add(-xf, interm, PI_2));
+    return fputil::cast<float16>(fputil::multiply_add(-xf, interm, PI_OVER_2));
   }
 
   // When |x| > 0.5, assume that 0.5 < |x| <= 1