util: add class for storing extensions strings

This utility will be used in future commits.

Also add -Wno-undefined to the linker flags to prevent leaving
undefined symbols in the layer .so file. Fix issues highlighted while
using this flag.

Change-Id: I682e266f7b3f313742cb2da83e5ad2569fc72da3
Signed-off-by: Joe Jenner-Bailey <joe.jenner-bailey@arm.com>
Signed-off-by: Matteo Franchin <matteo.franchin@arm.com>
Signed-off-by: Rosen Zhelev <rosen.zhelev@arm.com>
1 job for master in 1 minute and 55 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #6809658
build_vulkan_wsi_layer

00:01:55