PR 4935.
* parse.cxx (parser::parse_probe_point): Parse "if" condition
following probe point.
* staptree.h (probe_point): Add "condition" field.
(probe): Add "condition" field and "add_condition" method.
(deep_copy_visitor): Add "deep_copy" method for the expression.
* staptree.cxx (probe_point::probe_point): Initalize it.
(probe::add_condition): Implement it.
(probe::print): Output "condition" field.
(probe::str): Ditto.
(deep_copy_visitor::deep_copy): Implement it.
* elaborate.h (derived_probe): Add "insert_condition_statement"
method.
* elaborate.cxx (derived_probe::derived_probe): Initialize "condition"
field, and insert a condition check routine on the top of body.
(derived_probe::insert_condition_statement): Implement it.
(alias_expansion_builder::build): Pass the condition from the alias
referer to new alias.
* tapsets.cxx (be_derived_probe): Remove unused constructor.
(dwarf_derived_probe::dwarf_derived_probe): Insert a condition check
routine on the top of body.
(mark_derived_probe::mark_derived_probe): Ditto.
(mark_builder::build): Pass the base location to mark_derived_probe.