Ninja,Makefile: Move builtin linker flags to <LINK_FLAGS> placeholder
Previously we used separate placeholders for builtin linker flags:
* CMAKE_<LANG>_LINK_FLAGS for EXECUTABLEs
* CMAKE_SHARED_LIBRARY_CREATE_<LANG>_FLAGS for SHARED libraries
* CMAKE_SHARED_MODULE_CREATE_<LANG>_FLAGS for MODULE libraries
These correspond to variables set by our compiler information modules.
Teach the generators to look up these variables and add them to the
existing `<LINK_FLAGS>` placeholder instead. Substitute the empty
string for the old placeholders.
Issue: #21934
4 files changed
