Osu/mv2 hwloc2 (#36325)

* Revert "Remove legacy yaml from buildcache fetch (#34347)"
  This reverts commit b58ec9e2b9.
* Revert "Revert "Remove legacy yaml from buildcache fetch (#34347)""
  This reverts commit f91ec2e8da.
* add variant for hwloc v2
* running black

---------

Co-authored-by: Matt Lieber <lieber.31@osu.edu>

var/spack/repos/builtin/packages/mvapich2/package.py

@@ -108,6 +108,7 @@ class Mvapich2(AutotoolsPackage):
         "alloca", default=False, description="Use alloca to allocate temporary memory if available"
     )
 
+    variant("hwlocv2", default=False, description="Builds mvapich2 with hwloc v2")
     variant(
         "file_systems",
         description="List of the ROMIO file systems to activate",
@@ -430,6 +431,8 @@ def configure_args(self):
         else:
             args.append("--disable-cuda")
 
+        if "+hwlocv2" in self.spec:
+            args.append("--with-hwloc=v2")
         if "+regcache" in self.spec:
             args.append("--enable-registration-cache")
         else: