Bug 1316879 - Don't use CPP/CXXCPP from environment after bug 1299919. r=glandium

MozReview-Commit-ID: 4Of9nsVWK3q

--HG--
extra : rebase_source : 27724098df74dcff33ff5a8113200355ae287ae6

build/buildconfig.py

@@ -16,5 +16,5 @@ for var in ('topsrcdir', 'topobjdir', 'defines', 'non_global_defines',
 substs = dict(substs)
 
 for var in os.environ:
-    if var != 'SHELL' and var in substs:
+    if var not in ('CPP', 'CXXCPP', 'SHELL') and var in substs:
         substs[var] = os.environ[var]