[analyzer] New checker for detecting usages of unsafe I/O functions

There are certain unsafe or deprecated (since C11) buffer handling
functions which should be avoided in safety critical code. They
could cause buffer overflows. A new checker,
'security.insecureAPI.DeprecatedOrUnsafeBufferHandling' warns for
every occurrence of such functions (unsafe or deprecated printf,
scanf family, and other buffer handling functions, which now have
a secure variant).

Patch by Dániel Kolozsvári!

Differential Revision: https://reviews.llvm.org/D35068

llvm-svn: 353698