package/gdal: fix build without NPTL

Fix the following build failure without NPTL raised since the addition
of the package in commit 1e64fa29:

/tmp/instance-7/output-1/build/gdal-3.5.2/port/cpl_multiproc.cpp: In function 'CPLSpinLock* CPLCreateSpinLock()':
/tmp/instance-7/output-1/build/gdal-3.5.2/port/cpl_multiproc.cpp:2265:9: error: 'pthread_spin_init' was not declared in this scope; did you mean 'pthread_cond_init'?
 2265 |         pthread_spin_init(&(psSpin->spin), PTHREAD_PROCESS_PRIVATE) == 0 )
      |         ^~~~~~~~~~~~~~~~~
      |         pthread_cond_init

Fixes:
 - http://autobuild.buildroot.org/results/aa2a88990a07e551c40efb0c2180768add600c4f



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>