build(cmake): minor tweaks

[Tachi107]

• Enable THREADS_PREFER_PTHREAD_FLAG to use -pthread where supported
• Remove low-level compile features (closes Fix Compiling with Clang for CMake #1272)
• Remove unneeded DESTINATION options where possible

CC: @sum01

[sum01]

Looks good.

I don't understand the point in changing DESTINATION, but it's not important I guess. I just say this because TYPE INCLUDE seems to evaluate to read from CMAKE_INSTALL_INCLUDEDIR anyways (if I'm reading the docs right).

As for the prefer pthread flag, is there a reason for that? I'm just curious.
I know a long time ago I couldn't get things to compile without it (on Linux) but it seems to have since been a non-issue.

[Tachi107]

I don't understand the point in changing DESTINATION, but it's not important I guess. I just say this because TYPE INCLUDE seems to evaluate to read from CMAKE_INSTALL_INCLUDEDIR anyways

Yes, you're right, but it makes the code a bit cleaner (quite subjective but whatever, I can revert it if you prefer)

As for the prefer pthread flag, is there a reason for that? I'm just curious.

Yes. The first is that the docs "highly recommend" its usage where possible (i.e. In all projects targeting CMake >= 3.1), the second is that it's also the recommended way of enabling pthreads on compiler that support the flag, like GCC (according to their docs). Simply linking to -lpthread isn't always enough as the pthreads headers could require some macro like REENTRANT (or similar) to be defined, and a linker flag of course doesn't define that. So -pthread takes care of defining the necessary macros and linking to the necessary libraries.

[sum01]

Thanks for the response. You don't need to change the TYPE INCLUDE, it's fine.

[yhirose]

@Tachi107, is everything ready for merge?

[Tachi107]

Yes

[yhirose]

Thanks for your help!