select the system certificates more reliably

The rust build requires cargo to connect to its servers, it needs system
certificates to connect through MITM proxies or other various issues in
corporate systems.  This searches for more common locations to find
those certificates and the name used by RHEL in addition to the usual
debian convention.  Fixes rust build on TOSS4.

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

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 import re
+import os
 
 from spack.package import *
 
@@ -92,8 +93,16 @@ def setup_build_environment(self, env):
         env.set("AR", ar.path)
 
         # Manually inject the path of openssl's certs for build.
-        certs = join_path(self.spec["openssl"].prefix, "etc/openssl/cert.pem")
-        env.set("CARGO_HTTP_CAINFO", certs)
+        certs = None
+        for p in ("etc/openssl/cert.pem", "../etc/openssl/cert.pem",
+                  "etc/ssl/certs/ca-bundle.crt", "../etc/ssl/certs/ca-bundle.crt"):
+            certs = join_path(self.spec["openssl"].prefix, p)
+            if os.path.exists(certs):
+                break
+            else:
+                certs = None
+        if certs is not None:
+            env.set("CARGO_HTTP_CAINFO", certs)
 
     def configure(self, spec, prefix):
         opts = []