Trivial: Style fix

make the style checker happy

seL4_libs: remove autoconf.h from seL4_libs

this commit removes autoconf.h generation from each lib and
append '#include <<lib_name>/gen_config.h>' after each
'#include <autoconf.h>' since autoconf.h is only the for the
kernel config now. This is a temporarily solution, since we
currently don't have a way to tell which header files each file
is trying to include when it includes 'autoconf.h'

libsel4test: remove redundant config_set

This call needs to be guarded by an #ifdef, which is now there, so
remove the redundant config_set.

libsel4test: guard call to seL4_BenchmarkResetLog() by CONFIG_ENABLE_BENCHMARKS

Fix compilation failure about missing function seL4_BenchmarkResetLog(), which is defined only if CONFIG_ENABLE_BENCHMARKS is set.

libsel4test: Reset log if benchmarks are enabled

sel4test: trivial, minor style fixes

sel4test: refactor test result status into an enum

This allows tests to specify SUCCESS, FAILURE or ABORT. ABORT indicates
a fatal failure where the tests must stop. It replaces two global
variables to simplify and reduce global state.

It also changes sel4test_start_new_test to sel4test_reset, which resets
the state of the global variables in this library used for tracking the
current test_result_t.

is_aborted is removed as its no longer neccessary.

sel4test: simplify output buffering

- remove BUFFER_OUTPUT, as PRINT_XML implies it
- use config_set where possible
- replace interface with the following:
sel4test_start_printf_buffer: start buffering output
sel4test_end_printf_buffer: dump output and stop buffering
- remove a lot of ifdefs. sel4test is not build for performance
and its
best we compile as much code as possible.
sel4test_start_printf_buffer
does nothing if PRINT_XML is not enabled.

SELFOUR-642 move parts of libsel4test that depend on other libraries to
sel4test/libsel4testsupport

Rename `prototype.h` to `testutil.h` and `test.c` to `testutil.c`.