Since commit 2e1149874d (cmSystemTools: Support multiple binary formats,
2021-06-14, v3.22.0-rc1~575^2) the `file(RPATH_...)` operations fail on
files that are not ELF or XCOFF format. Previously the RPATH operations
tolerated files of unknown format if the goal was to produce a file with
an empty RPATH. Restore this tolerance in order to support setting an
empty RPATH on GNU ld scripts.
Fixes: #22963
Use ELF headers vendored in `Utilities/cmelf` to get the ELF constants
and types. Using the same ELF definition header for all compilation
targets allows removing some #ifdefs depending on the host OS since we
know all required ELF constants will always be present. To reduce the
size of this commit, the CMake_USE_ELF_PARSER definite will be removed
in a separate commit.
This allows me to use CMAKE_BUILD_WITH_INSTALL_RPATH=False and the Ninja
generator on macOS, whereas before it would always give me the following
error message (despite cross-compiling for an ELF-based platform):
```
The install of the <name> target requires changing an RPATH from
the build tree, but this is not supported with the Ninja generator unless
on an ELF-based platform. The CMAKE_BUILD_WITH_INSTALL_RPATH variable may
be set to avoid this relinking step.
```
Brad King