Work around a valgrind oddity where it doesn't pass the full path of a

script to the #! command by using bash instead of /bin/sh.  Bash
searches $PATH for its script argument, but dash, which /bin/sh
resolves to on some systems, does not.
https://bugs.kde.org/show_bug.cgi?id=231257 tracks the valgrind
problem.

llvm-svn: 98892