variables should have that linkage.  Otherwise, its static local
variables should have internal linkage.  To avoid computing this excessively,
set a function's linkage before we emit code for it.

Previously we were assigning weak linkage to the static variables of
static inline functions in C++, with predictably terrible results.  This
fixes that and also gives better linkage than 'weak' when merging is required.

llvm-svn: 104581