cmake: set -d postfix for debug builds if not specified

[snikulov]

Set -d postfix for debug builds if -DCMAKE_DEBUG_POSTFIX not specified

fixes #2121, obsoletes #2384

[snikulov]

@bradking Brad, could you please review?
Thank you in advance.

[bradking]

LGTM!

[snikulov]

@bradking Thank you!

[snikulov]

@bagder Daniel, can I merge this PR?

[bagder]

👍

[andyleejordan]

Just FYI this had the (probably unintended) side effect of no longer ever adding -d to the executable's name, only libraries, as CMAKE_DEBUG_POSTFIX applies only to non-executable targets automatically, and the explicit addition of it to the executable target was removed.

[bradking]

Typically debug suffixes aren't used for executables because the executables are used only locally for debugging. The purpose of a debug suffix on a library is to allow it to be installed adjacent to the non-debug variant of the library without colliding so that other executables can use it for debugging.

[andyleejordan]

Oh I agree, it makes no sense to add -d to an executable, and this is working as intended as far as CMake is concerned. I'm just saying that between the release of 7.60 and 7.61 of curl, the build behavior changed. The prior release did postfix the executable name, and I tracked it down to this when trying to integrate the update.