Fixes Android build by using C++ math header instead of C one.

runtime/vm/assembler_arm64_test.cc

Index: runtime/vm/assembler_arm64_test.cc
===================================================================
--- runtime/vm/assembler_arm64_test.cc	(revision 37827)
+++ runtime/vm/assembler_arm64_test.cc	(working copy)
@@ -3036,9 +3036,9 @@
 // This is the same function as in the Simulator.
 static float arm_recip_estimate(float a) {
   // From the ARM Architecture Reference Manual A2-85.
-  if (isinf(a) || (fabs(a) >= exp2f(126))) return 0.0;
+  if (std::isinf(a) || (fabs(a) >= exp2f(126))) return 0.0;
   else if (a == 0.0) return INFINITY;
-  else if (isnan(a)) return a;
+  else if (std::isnan(a)) return a;
 
   uint32_t a_bits = bit_cast<uint32_t, float>(a);
   // scaled = '0011 1111 1110' : a<22:0> : Zeros(29)
@@ -3145,9 +3145,9 @@
 
 static float arm_reciprocal_sqrt_estimate(float a) {
   // From the ARM Architecture Reference Manual A2-87.
-  if (isinf(a) || (fabs(a) >= exp2f(126))) return 0.0;
+  if (std::isinf(a) || (fabs(a) >= exp2f(126))) return 0.0;
   else if (a == 0.0) return INFINITY;
-  else if (isnan(a)) return a;
+  else if (std::isnan(a)) return a;
 
   uint32_t a_bits = bit_cast<uint32_t, float>(a);
   uint64_t scaled;