[OpenMP] Fix KMP_DYNAMIC_LIB to be dependent on LIBOMP_ENABLE_SHARED

The KMP_DYNAMIC_LIB guard was hard set to 1. This patch has the guard depend
on CMake variable LIBOMP_ENABLE_SHARED.


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@343866 91177308-0d34-0410-b5e6-96231b3b80d8