The 'base-linux' API is used by hybrid Genode/Linux programs for the
lx_hybrid library. This API archive happend to contain other libraries -
like seccomp - that are solely needed for building core. With the change
of the build system in issue #4599, the build system would attempt to
build all libraries instead of merely the library dependencies of the
available targets. Hence, it would trigger the build of, e.g., the
seccomp library for each user of the base-linux API.
This patch avoids these superfluous build steps by pruning the content
of lib/mk/ to the libraries actually needed for lx_hybrid users.
Issue #4599
The kernel-agnostic 'Trace::timestamp' function for arm_64 executes the
'mrs %0, pmccntr_el0' instruction, which is not permitted for user-level
programs on Linux. This patch shadows the generic timestamp.h header
with dummy that returns zero. This return value prompts the timeout
framework to disable the interpolation of time based on timestamps. This
avoid the illegal-instruction abort but comes with two llimitations:
First, time measurements are effectlively limited to a granulariry of 1
millisecond (deliberately constrained by the timer driver).
The quirk is applied when using the base-linux API. Should a generic
application (that uses the base API only) call 'Trace::timestamp'
directly, the illegal instruction is executed.
Issue #4136
