heaptrack on ~linux

[René J.V. Bertin]

Hi,

Can't we make the `add_subdirectory(heaptrack)` line in plugins/CMakeLists.txt conditional on being on Linux, IOW, something like

IF(UNIX AND NOT (APPLE OR CYGWIN))
    add_directory(heaptrack)
ENDIF()

it's a minor annoyance but it's also getting old seeing warnings about not-found dependencies which won't ever be available...

(I'd have pushed this directly but wasn't entirely sure about the exact check to make since CMake apparently has no specific Linux host variable.)

R.