tests: fix uClibc for getversion.c

This patch fixes compilation with uClibc by applying the same fallback
as commit e12d76176d4e5454db62eb48b58ecd4970838a76 to the getversion.c
file, which was previously overlooked.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: José Luis Salvador Rufo <salvador.joseluis@gmail.com>
Closes #16735
Closes #16741