[build] use the default TARGETS installation folder when possible
[build] use the default TARGETS installation folder when possible

It is implied by each target type (static and dynamic libraries here):

> For regular executables, static libraries and shared libraries, the
> DESTINATION argument is not required. For these target types, when
> DESTINATION is omitted, a default destination will be taken from the
> appropriate variable from GNUInstallDirs, or set to a built-in default value
> if that variable is not defined.

https://cmake.org/cmake/help/v3.14/command/install.html#targets

ethouris/srt,Haivision/srt,Haivision/srt,Haivision/srt,ethouris/srt,ethouris/srt,ethouris/srt,Haivision/srt