analyzer: support "_IO_"-prefixed variants of FILE * fns [PR98575]

analyzer: support "_IO_"-prefixed variants of FILE * fns [PR98575]

PR analyzer/98575 describes an unexpected -Wanalyzer-malloc-leak false
positive from gcc.dg/analyzer/pr94851-1.c on glibc < 2.28.

The issue is that a getchar call gets inlined into a call to _IO_getc,
and "_IO_getc" is not in the set of FILE * functions the analyzer
"knows about".  This exposes a bug in memory leak detection on code
paths in which an unknown function has been called.

The memory leak bug is fixed in the prior commit, but for good
measure this patch special-cases the "_IO_"-prefixed names in glibc
so that the analyzer can reuse its knowledge about the unprefixed
variants.

gcc/analyzer/ChangeLog:
	PR analyzer/98575
	* sm-file.cc (is_file_using_fn_p): Support "_IO_"-prefixed
	variants.

gcc/testsuite/ChangeLog:
	PR analyzer/98575
	* gcc.dg/analyzer/file-1.c (test_5): New.
	* gcc.dg/analyzer/file-3.c: New test.