cmake: allow using system-installed readerwriterqueue #157
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readerwriterqueue
can be installed into system directories, and a number of distributions already package it. Where possible, use the system-provided copy rather than requiring it to be downloaded viaFetchContent
.Currently the default behavior provided by this PR is to use the system-provided copy if available; if preferred, this can also be inverted to prefer the
FetchContent
and only rely on the system version via an explicit option.The objective of this PR is to allow downstream packagers to rely on their own system-installed copies of dependencies where possible rather than have them be downloaded at compile time. (I'd like to do the same for
ni-midi2
, but the build system forni-midi2
does not yet facilitate installing it into system directories.)If this change is not accepted, downstream packagers can still point
FetchContent
to a system-provided copy ofreaderwriterqueue
, e.g.-DFETCHCONTENT_SOURCE_DIR_READERWRITERQUEUE:PATH=/usr/lib/cmake/readerwriterqueue
.