Recognize .ll as input files.

Handle %test_debuginfo on a RUN command line.

This set up now allows one to write small test cases to check debug info.
e.g.

; RUN: %clang -O0 -g %s -c -o %t.o
; RUN: %clang %t.o -o %t.out  
; RUN: %test_debuginfo %s %t.out

define i32 @f1(i32 %i) nounwind ssp {
; DEBUGGER: break f1                                                               
; DEBUGGER: r                                                                      
; DEBUGGER: p i                                                                    
; CHECK: $1 = 42                                                                   
entry:
  %i.addr = alloca i32, align 4
...
...
}

It is also possible now to write test cases in c/c++.
The plan is to store these debug info testcases in a separate place.

llvm-svn: 113780