Fix large overhead with itt notifications on region/barrier name composing

Currently, there is a big overhead in reporting of loop metadata through
ittnotify.  The pair of functions: __kmp_str_loc_init/__kmp_str_loc_free are
replaced with strchr/atoi calls.  Thus, a lot of time consuming actions are
skipped - many memory allocations/deallocations, heavy string duplication, etc.
The loop metadata only needs line and column info from the source string, so no
allocations and string splitting actually needed.

Patch by Andrey Churbanov

Differential Revision: http://reviews.llvm.org/D21309

llvm-svn: 272698