Devtools darwin (#46910)

* stacks: add a stack for devtools on darwin

After getting this whole mess building on darwin, let's keep it that
way, and maybe make it so we have some non-ML darwin binaries in spack
as well.

* reuse: false for devtools

* dtc: fix darwin dylib name and id

On mac the convention is `lib<name>.<num>.dylib`, while the makefile
creates a num suffixed one by default. The id in the file is also a
local name rather than rewritten to the full path, this fixes both
problems.

* node-js: make whereis more deterministic

* relocation(darwin): catch Mach-O load failure

The MachO library can throw an exception rather than return no headers,
this happened in an elf file in the test data of go-bootstrap.  Trying
catching the exception and moving on for now.  May also need to look
into why we're trying to rewrite an elf file.

* qemu: add darwin flags to clear out warnings

There's a build failure for qemu in CI, but it's invisible because of
the immense mass of warning output.  Explicitly specify the target macos
version and remove the extraneous unknown-warning-option flag.

* dtc: libyaml is also a link dependency

libyaml is required at runtime to run the dtc binary, lack of it caused
the ci for qemu to fail when the library wasn't found.

lib/spack/spack/relocate.py

@@ -283,7 +283,11 @@ def modify_macho_object(cur_path, rpaths, deps, idpath, paths_to_paths):
 
 def macholib_get_paths(cur_path):
     """Get rpaths, dependent libraries, and library id of mach-o objects."""
-    headers = macholib.MachO.MachO(cur_path).headers
+    headers = []
+    try:
+        headers = macholib.MachO.MachO(cur_path).headers
+    except ValueError:
+        pass
     if not headers:
         tty.warn("Failed to read Mach-O headers: {0}".format(cur_path))
         commands = []