test_clang: initialize format string arg on stack
test_clang: initialize format string arg on stack

With local LLVM (4.0ish), inline strings in this test case would
segfault. Fix the crash by constructing explicitly on the stack.

Signed-off-by: Brenden Blanco <8e41c261aa8ddb01230a40c21c26a049c1f6d041@gmail.com>

iovisor/bcc,mcaleavya/bcc,mcaleavya/bcc,iovisor/bcc,shodoco/bcc,shodoco/bcc,tuxology/bcc,tuxology/bcc,tuxology/bcc,brendangregg/bcc,brendangregg/bcc,romain-intel/bcc,iovisor/bcc,tuxology/bcc,iovisor/bcc,shodoco/bcc,iovisor/bcc,mcaleavya/bcc,romain-intel/bcc,romain-intel/bcc,shodoco/bcc,brendangregg/bcc,brendangregg/bcc,romain-intel/bcc,romain-intel/bcc,mcaleavya/bcc,tuxology/bcc,shodoco/bcc,mcaleavya/bcc,brendangregg/bcc