[wpiutil] timestamp: Call FPGA functions directly (#5235)

This works around an exit race with wpi::Now() on Rio; it was overridden
to call HAL_GetFPGATime(), which calls chipobject, but on exit, because
there was not a library dependency, the chipobject could be destroyed
prior to wpiutil/wpinet being shut down.

wpiutil/src/main/native/include/wpi/timestamp.h

@@ -11,6 +11,13 @@
 extern "C" {
 #endif
 
+/**
+ * Initialize the on-Rio Now() implementation to use the FPGA timestamp.
+ * No effect on non-Rio platforms. This is called by HAL_Initialize() and
+ * thus should generally not be called by user code.
+ */
+void WPI_Impl_SetupNowRio(void);
+
 /**
  * The default implementation used for Now().
  * In general this is the time returned by the operating system.
@@ -48,12 +55,21 @@ uint64_t WPI_GetSystemTime(void);
 #ifdef __cplusplus
 namespace wpi {
 
+namespace impl {
+/**
+ * Initialize the on-Rio Now() implementation to use the FPGA timestamp.
+ * No effect on non-Rio platforms. This is called by HAL_Initialize() and
+ * thus should generally not be called by user code.
+ */
+void SetupNowRio();
+}  // namespace impl
+
 /**
  * The default implementation used for Now().
  * In general this is the time returned by the operating system.
  * @return Time in microseconds.
  */
-uint64_t NowDefault(void);
+uint64_t NowDefault();
 
 /**
  * Set the implementation used by Now().
@@ -68,7 +84,7 @@ void SetNowImpl(uint64_t (*func)());
  * This is a monotonic clock with an undefined epoch.
  * @return Time in microseconds.
  */
-uint64_t Now(void);
+uint64_t Now();
 
 /**
  * Return the current system time in microseconds since the Unix epoch