[OPENMP] Temporary fix for processing of global variables in loops.

Currently there is a bug in processing of global variables used as loop control variables in 'omp for/simd' constructs: these globals must be captured as private variables, but currently they are nor. This is a temporary bug fix for this problem until the correct solution is prepared. If a global var used as lcv without explicit mark as a private/linear/lastprivate the error message is emitted.

llvm-svn: 221970