mariadb: needs dynamic library support

mariadb: needs dynamic library support

In a static-only configuration, mariadb fails to build because it
tries to build a shared library:

[ 18%] Linking CXX shared module ha_spider.so
output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/6.4.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: output/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/6.4.0/../../../../arm-buildroot-linux-uclibcgnueabi/lib/libstdc++.a(eh_globals.o)(.text.__cxa_get_globals_fast+0x14): R_ARM_TLS_LE32 relocation not permitted in shared object

This is not detected by the autobuilders, because mariadb is part of a
Config.in choice, and such choices are not randomized by our current
testing infrastructure.

Signed-off-by: Ryan Coe <bluemrp9@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>