Fix bungled parse recovery in K&R function declarations

  void knrNoSemi(i) int i { }

Adherents of The C Programming Language unfortunate enough to miss a semicolon
as above would be met with a cascade of errors spanning the remainder of the
TU.

This patch introduces a beautiful parse error recovery, complete with helpful
FixIt to restore sanity.

Before (output redacted for brevity):

  error: 'error' diagnostics seen but not expected:
    File declarators.c Line 119: declaration does not declare a parameter
    File declarators.c Line 123: declaration does not declare a parameter
    File declarators.c Line 127: parameter named 'func_E12' is missing
    File declarators.c Line 127: expected ';' at end of declaration
    File declarators.c Line 133: parameter named 'func_E13' is missing
    File declarators.c Line 133: expected ';' at end of declaration
    File declarators.c Line 139: parameter named 'func_E14' is missing
    File declarators.c Line 139: expected ';' at end of declaration
    File declarators.c Line 145: parameter named 'func_E15' is missing
    File declarators.c Line 145: expected ';' at end of declaration
    File declarators.c Line 150: expected function body after function declarator
    File declarators.c Line 119: declaration of 'enum E11' will not be visible outside of this function
    File declarators.c Line 123: declaration of 'enum E12' will not be visible outside of this function
    File declarators.c Line 133: ISO C forbids forward references to 'enum' types
    File declarators.c Line 133: declaration of 'enum E13' will not be visible outside of this function
    File declarators.c Line 139: ISO C forbids forward references to 'enum' types
    File declarators.c Line 139: declaration of 'enum E14' will not be visible outside of this function
    File declarators.c Line 145: ISO C forbids forward references to 'enum' types
    File declarators.c Line 145: declaration of 'enum E15' will not be visible outside of this function
    ...

After:

  declarators.c:103:24: error: expected ';' at end of declaration
  void knrNoSemi(i) int i { }
                         ^
                         ;

Patch found in a sealed envelope dated 1978 with the message "Do not open until
January 2014"

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198540 91177308-0d34-0410-b5e6-96231b3b80d8