package/opencv: fix build with old glibc versions

Prior to glibc 2.18, definitions like SIZE_MAX or INT_FAST32_MAX from
<stdint.h> were only made available for C code, or in C++ if
__STDC_LIMIT_MACROS was defined.

The code from jasper uses such definitions, without defining
__STDC_LIMIT_MACROS. Unfortunately, defining __STDC_LIMIT_MACROS in
the jasper headers doesn't work, since <stdint.h> has already been
included before, at a point where __STDC_LIMIT_MACROS was not defined.

So to solve this problem, we simply pass -D__STDC_LIMIT_MACROS in
CXXFLAGS when building opencv with jasper support.

This patch uses the same solution used for libraw:
https://git.buildroot.net/buildroot/commit/package/libraw?id=d246cf5fd01bb0d20a0e64194ffed514ea8dd0aa

Fixes:
http://autobuild.buildroot.net/results/095/095f7574afdb633c59a625cd063de03644b6d3a7/



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>