28d76590f1
Instead of setting a string property to magic default value and then
checking for it later, call ctx.ContainsProperty to determine if it
was set. Use the same method on the clang bool property, which
couldn't be set to a magic value.
blueprint's ModuleContext.ContainsProperty only works on a single
property, not on all arch variant properties -
ModuleContext.ContainsProperty("clang") will return false if
clang was not set but arch.arm.clang was set - so track which
properties were extended inside extendProperties, and override
ModuleContext.ContainsProperty in AndroidModuleContext to also
check the extended properties.
Change-Id: I03cbe71dc69344972e23d6c794da9be05e720c45