package/openal: needs gcc >= 4.9

package/openal: needs gcc >= 4.9

openal uses std::max_align_t since version 1.20.0 and
https://github.com/kcat/openal-soft/commit/585b0cf3bed7d1c5720633eb7e5358a9fca865f6

As a result, it is affected by
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56019
and the build with gcc <= 4.8 will fail on:

/home/buildroot/autobuild/instance-2/output-1/build/openal-1.20.1/common/almalloc.cpp: In function 'void* al_malloc(size_t, size_t)':
/home/buildroot/autobuild/instance-2/output-1/build/openal-1.20.1/common/almalloc.cpp:20:45: error: 'max_align_t' is not a member of 'std'
     alignment = std::max(alignment, alignof(std::max_align_t));
                                             ^

Fixes:
 - http://autobuild.buildroot.org/results/589c7853ce334c7502f7cd4cdbcaaf3c6840f43b

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