cmake: fix invalid syntax when generating version.h from tags

When building from git tags, the version number in `include/version.h`
is extracted from the output of `git describe`. While that is correct,
cmake was not configured to strip trailing whitespace from the command
output, which resulted in the version number being `12.5.1\n`.

That broke the generation of `include/version.h`, as the `\n` resulted
in the terminating quote being in a new line. This commit fixes that by
instructing cmake to strip trailing whitespace.

cmake/nuttx_mkversion.cmake

@@ -28,7 +28,8 @@ execute_process(
   WORKING_DIRECTORY ${NUTTX_DIR}
   ERROR_VARIABLE NUTTX_ERROR
   OUTPUT_VARIABLE NUTTX_VERSION
-  RESULT_VARIABLE VERSION_STATUS)
+  RESULT_VARIABLE VERSION_STATUS
+  OUTPUT_STRIP_TRAILING_WHITESPACE)
 
 if(${VERSION_STATUS} AND NOT ${VERSION_STATUS} EQUAL 0)
   set(NUTTX_VERSION "0.0.0")