drv_hrt: inline hrt_elapsed_time

GCC did not do that.

platforms/posix/src/px4_layer/drv_hrt.cpp

@@ -198,19 +198,6 @@ hrt_abstime ts_to_abstime(const struct timespec *ts)
 	return result;
 }
 
-/*
- * Compute the delta between a timestamp taken in the past
- * and now.
- *
- * This function is safe to use even if the timestamp is updated
- * by an interrupt during execution.
- */
-hrt_abstime hrt_elapsed_time(const hrt_abstime *then)
-{
-	hrt_abstime delta = hrt_absolute_time() - *then;
-	return delta;
-}
-
 /*
  * Compute the delta between a timestamp taken in the past
  * and now.

src/drivers/drv_hrt.h

@@ -98,7 +98,10 @@ __EXPORT extern void	abstime_to_ts(struct timespec *ts, hrt_abstime abstime);
  *
  * This function is not interrupt save.
  */
-__EXPORT extern hrt_abstime hrt_elapsed_time(const hrt_abstime *then);
+static inline hrt_abstime hrt_elapsed_time(const hrt_abstime *then)
+{
+	return hrt_absolute_time() - *then;
+}
 
 /**
  * Compute the delta between a timestamp taken in the past

src/drivers/kinetis/drv_hrt.c

@@ -594,17 +594,6 @@ abstime_to_ts(struct timespec *ts, hrt_abstime abstime)
 	ts->tv_nsec = abstime * 1000;
 }
 
-/**
- * Compare a time value with the current time.
- */
-hrt_abstime
-hrt_elapsed_time(const hrt_abstime *then)
-{
-	hrt_abstime delta = hrt_absolute_time() - *then;
-
-	return delta;
-}
-
 /**
  * Compare a time value with the current time as atomic operation.
  */

src/drivers/samv7/drv_hrt.c

@@ -675,17 +675,6 @@ abstime_to_ts(struct timespec *ts, hrt_abstime abstime)
 	ts->tv_nsec = abstime * 1000;
 }
 
-/**
- * Compare a time value with the current time.
- */
-hrt_abstime
-hrt_elapsed_time(const hrt_abstime *then)
-{
-	hrt_abstime delta = hrt_absolute_time() - *then;
-
-	return delta;
-}
-
 /**
  * Compare a time value with the current time as atomic operation.
  */

src/drivers/stm32/drv_hrt.c

@@ -715,17 +715,6 @@ abstime_to_ts(struct timespec *ts, hrt_abstime abstime)
 	ts->tv_nsec = abstime * 1000;
 }
 
-/**
- * Compare a time value with the current time.
- */
-hrt_abstime
-hrt_elapsed_time(const hrt_abstime *then)
-{
-	hrt_abstime delta = hrt_absolute_time() - *then;
-
-	return delta;
-}
-
 /**
  * Compare a time value with the current time as atomic operation
  */