autotools/siteinfo: Avoid races over siteinfo files

If a siteinfo enabled tasks re-executes at the wrong moment whilst something else is
in do_configure, the _config files can be removed which upsets autoconf and
causes build failures.

Use the same approach as we do for dealing with the aclocal files. We already
parse the manifests so look out any *_config files and if so, copy them, then
reference the copy from siteinfo instead. This has the advantage of also being
more deterministic.

[YOCTO #7101]

(From OE-Core rev: c8b7aad133c3e3319345d50f85a91cbd5116f842)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/siteinfo.bbclass

@@ -150,9 +150,13 @@ def siteinfo_get_files(d, no_cache = False):
     if no_cache: return sitefiles
 
     # Now check for siteconfig cache files
-    path_siteconfig = d.getVar('SITECONFIG_SYSROOTCACHE', True)
-    if os.path.isdir(path_siteconfig):
+    # Use the files copied to the aclocal cache generated by autotools.bbclass
+    # to avoid races
+    path_siteconfig = d.getVar('ACLOCALDIR', True)
+    if path_siteconfig and os.path.isdir(path_siteconfig):
         for i in os.listdir(path_siteconfig):
+            if not i.endswith("_config"):
+                continue
             filename = os.path.join(path_siteconfig, i)
             sitefiles += filename + " "