block: use per-object cflags and libs

block: use per-object cflags and libs

No longer adds flags and libs for them to global variables, instead
create config-host.mak variables like FOO_CFLAGS and FOO_LIBS, which is
used as per object cflags and libs.

This removes unwanted dependencies from libcacard.

Signed-off-by: Fam Zheng <[email protected]>
[Split from Fam's patch to enable modules. - Paolo]
Signed-off-by: Paolo Bonzini <[email protected]>
Signed-off-by: Fam Zheng <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>