Bug 1869998 - Port bug 1869078 - Filter-out target_cpu from substs provided by old-configure. rs=bustage-fix

https://hg.mozilla.org/mozilla-central/rev/722156e33a15 made lower-case target_cpu unavailable. Looks like we should've been using upper-case TARGET_CPU anyway.

--HG--
extra : amend_source : 23e2de96ef1469a0ee32ea09b8cbe7bc5637e0f9

third_party/botan/botan.mozbuild

@@ -44,7 +44,7 @@ if CONFIG['COMPILE_ENVIRONMENT']:
     botan_build.script = 'botan_configure.py'
     botan_build.flags = [
         '--cc-bin={}'.format(CONFIG['CXX']),
-        '--cpu={}'.format(CONFIG['target_cpu']),
+        '--cpu={}'.format(CONFIG['TARGET_CPU']),
         '--os={}'.format(botan_os),
         '--with-build-dir={}'.format(OBJDIR),
         '--minimized-build',