Add libstdc++-staticdev to target toolchain to support building
agl-service-voice-high or other users of the C++17 filesystem standard
library feature. This can be removed upon upgrade to gcc 9.x, as it
will no longer be necessary.
Bug-AGL: SPEC-2856, SPEC-2857
Change-Id: Ifd50d4e9960fe0bede887317116e6587eca5eb3d Signed-off-by: Scott Murray <scott.murray@konsulko.com>