Fix TestDataFormatter.test uninitialized variable

After D55626 I see a failure in my Fedora buildbot.

There is uninitialized variable as the Foo constructor has not been run and foo
is an autovariable.

(lldb) breakpoint set -f foo.cpp -l 11
Breakpoint 1: where = TestDataFormatter.test.tmp.out`main + 30 at foo.cpp:11:7, address = 0x000000000040112e
(lldb) run
Process 801065 stopped
* thread #1, name = 'TestDataFormatt', stop reason = breakpoint 1.1
    frame #0: 0x000000000040112e TestDataFormatter.test.tmp.out`main(argc=1, argv=0x00007fffffffcc48) at foo.cpp:11:7
   8   	};
   9
   10  	int main(int argc, char **argv) {
-> 11  	  Foo foo(1, 2.22);
   12  	  return 0;
   13  	}

Process 801065 launched: '.../tools/lldb/lit/Reproducer/Functionalities/Output/TestDataFormatter.test.tmp.out' (x86_64)
(lldb) frame var
(int) argc = 1
(char **) argv = 0x00007fffffffcc48
(Foo) foo = (m_i = 4198432, m_d = 0)

While the testcase expects m_i will be 0.

Differential Revision: https://reviews.llvm.org/D59088

llvm-svn: 355611