Workaround MSVC STL deficiency in C++17 mode

Compiling jet_test using the /std:c++17 switch triggers a C3198 compile
error in <numeric>. Moving #pragma below all the includes, allows to
workaround the issue.

Additionally, locally ensure the floating-point model is always
/fp:precise to be able to access the floating-point environment in
jet_test.

Change-Id: Ia5b3a3dac13baf46546ac1d0d304fc05512f8816

internal/ceres/jet_test.cc

@@ -28,17 +28,6 @@
 //
 // Author: keir@google.com (Keir Mierle)
 
-// The floating-point environment access and modification is only meaningful
-// with the following pragma.
-#ifdef _MSC_VER
-#pragma fenv_access(on)
-#elif !(defined(__ARM_ARCH) && __ARM_ARCH >= 8)
-// NOTE: FENV_ACCESS cannot be set to ON when targeting arm(v8)
-#pragma STDC FENV_ACCESS ON
-#else
-#define CERES_NO_FENV_ACCESS
-#endif
-
 #include "ceres/jet.h"
 
 #include <Eigen/Dense>
@@ -52,6 +41,18 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
+// The floating-point environment access and modification is only meaningful
+// with the following pragma.
+#ifdef _MSC_VER
+#pragma float_control(precise, on, push)
+#pragma fenv_access(on)
+#elif !(defined(__ARM_ARCH) && __ARM_ARCH >= 8)
+// NOTE: FENV_ACCESS cannot be set to ON when targeting arm(v8)
+#pragma STDC FENV_ACCESS ON
+#else
+#define CERES_NO_FENV_ACCESS
+#endif
+
 namespace ceres {
 namespace internal {
 
@@ -1293,3 +1294,7 @@ TYPED_TEST(JetTest, Nested3XComparison) {
 
 }  // namespace internal
 }  // namespace ceres
+
+#ifdef _MSC_VER
+#pragma float_control(pop)
+#endif