Bugfix: cray manifest parsing regression (#37909)

fa7719a changed syntax for specifying exact versions, which are
required for some compiler specs (including those read as part
of parsing a Cray manifest). This fixes that and also makes a
couple other improvements to manifest parsing.

* Instantiate compiler specs with exact versions (fixes #37893)
* fix slingshot network detection (CPE 22.10+ has libcxi.so
  in /usr/lib64)
* "spack external find": add arg to ignore default dir for cray
  manifests

lib/spack/spack/cmd/external.py

@@ -79,6 +79,12 @@ def setup_parser(subparser):
     read_cray_manifest.add_argument(
         "--directory", default=None, help="specify a directory storing a group of manifest files"
     )
+    read_cray_manifest.add_argument(
+        "--ignore-default-dir",
+        action="store_true",
+        default=False,
+        help="ignore the default directory of manifest files",
+    )
     read_cray_manifest.add_argument(
         "--dry-run",
         action="store_true",
@@ -177,11 +183,16 @@ def external_read_cray_manifest(args):
         manifest_directory=args.directory,
         dry_run=args.dry_run,
         fail_on_error=args.fail_on_error,
+        ignore_default_dir=args.ignore_default_dir,
     )
 
 
 def _collect_and_consume_cray_manifest_files(
-    manifest_file=None, manifest_directory=None, dry_run=False, fail_on_error=False
+    manifest_file=None,
+    manifest_directory=None,
+    dry_run=False,
+    fail_on_error=False,
+    ignore_default_dir=False,
 ):
     manifest_files = []
     if manifest_file:
@@ -191,7 +202,7 @@ def _collect_and_consume_cray_manifest_files(
     if manifest_directory:
         manifest_dirs.append(manifest_directory)
 
-    if os.path.isdir(cray_manifest.default_path):
+    if not ignore_default_dir and os.path.isdir(cray_manifest.default_path):
         tty.debug(
             "Cray manifest path {0} exists: collecting all files to read.".format(
                 cray_manifest.default_path

lib/spack/spack/cray_manifest.py

@@ -48,7 +48,8 @@ def translated_compiler_name(manifest_compiler_name):
 def compiler_from_entry(entry):
     compiler_name = translated_compiler_name(entry["name"])
     paths = entry["executables"]
-    version = entry["version"]
+    # to instantiate a compiler class we may need a concrete version:
+    version = "={}".format(entry["version"])
     arch = entry["arch"]
     operating_system = arch["os"]
     target = arch["target"]

lib/spack/spack/platforms/cray.py

@@ -37,7 +37,9 @@
 
 
 def slingshot_network():
-    return os.path.exists("/opt/cray/pe") and os.path.exists("/lib64/libcxi.so")
+    return os.path.exists("/opt/cray/pe") and (
+        os.path.exists("/lib64/libcxi.so") or os.path.exists("/usr/lib64/libcxi.so")
+    )
 
 
 def _target_name_from_craype_target_name(name):