Keep including the full version.h when headers are included externally

This avoids unnecessary churn and build breakage for users, by
making sure the whole version.h is included like it has been so far,
while keeping the benefit of not needing to rebuild most files in
the ffmpeg tree on minor/micro bumps.

Signed-off-by: Martin Storsjö <martin@martin.st>

libswresample/swresample.h

@@ -126,6 +126,12 @@
 #include "libavutil/samplefmt.h"
 
 #include "libswresample/version_major.h"
+#ifndef HAVE_AV_CONFIG_H
+/* When included as part of the ffmpeg build, only include the major version
+ * to avoid unnecessary rebuilds. When included externally, keep including
+ * the full version information. */
+#include "libswresample/version.h"
+#endif
 
 /**
  * @name Option constants