analyzer: add function-set.cc/h

analyzer: add function-set.cc/h

This patch adds a simple mechanism for tracking sets of functions
for which a particular property holds, as a pragmatic way to build
knowledge about important APIs into the analyzer without requiring
markup of the user's libc.

gcc/ChangeLog:
	* Makefile.in (ANALYZER_OBJS): Add analyzer/function-set.o.

gcc/analyzer/ChangeLog:
	* analyzer-selftests.cc (selftest::run_analyzer_selftests): Call
	selftest::analyzer_function_set_cc_tests.
	* analyzer-selftests.h (selftest::analyzer_function_set_cc_tests):
	New decl.
	* function-set.cc: New file.
	* function-set.h: New file.