Fix hard-coded bash path in gprofng

When running 'make check', the default gprofng test suite creates a
shell script for which it used a hardcoded shebang of '/usr/bin/bash'
this script would not run if bash is in a different location, like
/bin/bash

This commit adds 'AC_PATH_PROG(BASH, bash)' to configure.ac so the
installation path of bash is detected at configuration time. The
configuration is propagated to the runtest command line where it is
needed.
8 files changed