Clang/libomptarget map interface flag renaming - NFC patch

This patch renames some of the flag names of the clang/libomptarget map interface. The old names are slightly misleading, whereas the new ones describe in a better way what each flag is about.

Only the macros within the enumeration are renamed, there is no change in functionality therefore there are no updated regression tests.

Differential Revision: https://reviews.llvm.org/D39745

llvm-svn: 317598