[PATCH] Add Position-independent Code model Module API.

[Rafael Ávila de Espíndola]

I think this is fine. We can always change the error to an merge logic in the future if needed. Eric, what do you think?

================
Comment at: test/Linker/module-flags-pic-2-a.ll:10
@@ +9,2 @@
+
+; CHECK-ERRORS: ERROR: WARNING: linking module flags 'flag_pic': IDs have conflicting values
----------------
I think I fixed the "EROR: WARNING" in another patch. This should be just ERROR now.

http://reviews.llvm.org/D5882