Allow running HPCToolkit out of the build tree

Currently using HPCToolkit requires installing it to some installation prefix first. This is a bit tedious for developers to do every time, and doesn't match "the sequence" defined by either Autotools or Meson. It would be nice if HPCToolkit could run from the build tree prior to installation.

Rationale

Both Autotools and Meson define the sequence of commands to be used to build software:

• Autotools: ./configure && make all/check/install/installcheck
• Meson: meson setup/compile/test/install

In both cases, tests are run before the software is installed. Unfortunately, since HPCToolkit can't be run uninstalled, we can't actually conform to the standard command sequences. This throws a curveball at new developers and builders, is non-conformant to how the build systems were intended to be used, and removes any "shortcuts" built into the build system assuming conformance (e.g. meson test automatically runs meson compile, but since we need meson install that does nothing for the tests).

Description

We need to be able to run the test suite without installing HPCToolkit. This means the build tree should contain working copies of hpcrun/hpcstruct/hpcprof/etc.