build: add DebugCoverage build type

Add a new build type to capture compiler flags settings needed for GCOV
based coverage measurement. This build type is only supported by
environments targeting Linux.
The aim is to allow extending coverage measurement to sub-builds
(especially libts).

Signed-off-by: Gyorgy Szing <gyorgy.szing@arm.com>
Change-Id: I1de619c0b96c1d2d519432458c3eac4aed947acf
3 files changed