[UniqueLinkageName] Use consistent checks when mangling symbo linkage name and debug linkage name.

C functions may be declared and defined in different prototypes like below. This patch unifies the checks for mangling names in symbol linkage name emission and debug linkage name emission so that the two names are consistent.

static int go(int);

static int go(a) int a;
{
  return a;
}

Test Plan:

Differential Revision: https://reviews.llvm.org/D98799