ust-compiler: constructor/destructor whitespaces layout and macro dependency

ust-compiler: constructor/destructor whitespaces layout and macro dependency

Introduce LTTNG_UST_COMPILER_COMBINE_TOKENS in lttng/ust-compiler.h to
eliminate a circular dependency from ust-compiler.h to
LTTNG_UST__TP_COMBINE_TOKENS (defined in tracepoint.h). Use it in
LTTNG_UST_DECLARE_CONSTRUCTOR_DESTRUCTOR.

Change the layout of LTTNG_UST_DECLARE_CONSTRUCTOR_DESTRUCTOR to use
tabs rather than spaces.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I71ecac349a1425401df62eb600ee74f4f930da09