In standard C since C89, a 'translation-unit' is syntactically defined to have
at least one "external-declaration", which is either a decl or a function
definition. In Clang the latter gives us a declaration as well.

The tricky bit about this warning is that our predefines can contain external
declarations (__builtin_va_list and the 128-bit integer types). Therefore our
AST parser now makes sure we have at least one declaration that doesn't come
from the predefines buffer.

Also, remove bogus warning about empty source files. This doesn't catch source
files that only contain comments, and never fired anyway because of our
predefines.

PR12665 and <rdar://problem/9165548>

llvm-svn: 158085

 - This is designed to make it obvious that %clang_cc1 is a "test variable"
   which is substituted. It is '%clang_cc1' instead of '%clang -cc1' because it
   can be useful to redefine what gets run as 'clang -cc1' (for example, to set
   a default target).

llvm-svn: 91446

Tests and drivers updated, still need to shuffle dirs.

llvm-svn: 67602

llvm-svn: 57068

zero tokens.  This fixes PR2045, thanks to Neil for finding another 
incredibly subtle corner case :)

llvm-svn: 47203