cmake: Follow-up on PR74

[hebasto]

This PR is a follow-up on #74.

No need to try a flag in the linker context if it is not supported in the compiler context.

For example, on the staging branch:

$ env CC=clang CXX=clang++ cmake -B build
...
-- Performing Test CXX_SUPPORTS__FSTACK_REUSE_NONE
-- Performing Test CXX_SUPPORTS__FSTACK_REUSE_NONE - Failed
CMake Warning at cmake/module/TryAppendCXXFlags.cmake:125 (message):
  The -fstack-reuse=none fail(s) to link.
Call Stack (most recent call first):
  CMakeLists.txt:310 (try_append_cxx_flags)


...

[hebasto]

cc @TheCharlatan @theuni @m3dwards @pablomartin4btc