Fix omlc_set_string() and omlc_set_const_string() macros.
Fix omlc_set_string() and omlc_set_const_string() macros.

- Didn't play well with code that expected them to comprise a
  single statement.
- Wrapped them in the usual do {...} while (0);

(cherry picked from commit 759a55d5df74bd81fdcc091297a9b68805104690)

alco90/soml,lees0414/EUproject,lees0414/EUproject,mytestbed/oml,mytestbed/oml,mytestbed/oml,lees0414/EUproject,alco90/soml,alco90/soml,mytestbed/oml,mytestbed/oml,alco90/soml,alco90/soml,lees0414/EUproject,lees0414/EUproject