Limit size of non-GlobalValue name

Otherwise, in some extreme test case, very long names are created and the
compiler consumes large amount of memory. Size limit is set to a relatively
high value not to disturb debugging.

Compiler flag -non-global-value-max-name-size=<value> can be used to customize
the size.

Differential Revision: https://reviews.llvm.org/D41296

llvm-svn: 321886