message: build_system: only use pragma with gcc
  This should fix the MSVC build.
diff: @@ -7,8 +7,10 @@ using namespace mavsdk;
  // We need to use strncpy without zero termination, so with possible
  // stringop-truncation here, on purpose because the MAVLink message structure
  // of statustext.text does not include the zero termination.
  +#if defined(__GNUC__)
  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wstringop-truncation"
  +#endif // defined(__GNUC__)
  TEST(MavlinkStatustextHandler, Severities)
  {
  @@ -266,4 +268,6 @@ TEST(MavlinkStatustextHandler, MultiStatustextConsecutive)
  }
  }
  +#if defined(__GNUC__)
  #pragma GCC diagnostic pop
  +#endif // defined(__GNUC__)
  