Revert "Fix for merging decls in pragma weak Calling CheckFunctionDeclaration...

Revert "Fix for merging decls in pragma weak Calling CheckFunctionDeclaration so that 2 decls for the 'weak' are merged. Differential Revision: http://reviews.llvm.org/D13048"

This reverts commit r254143 which introduces a crash on the following input:
  f(char *);
  g(char *);
  #pragma weak f = g
  int g(char *p) {}

llvm-svn: 254605