GNU make always defaults CC to "cc", so using "?=" with the CC variable
will never override the internal make value.  since @CC@ comes from the
configure script, and that respects the $CC env var, don't bother trying
to handle it in make too.  it's not like we do this with any other build
variable after all.

--- a/make.tmpl.in
+++ b/make.tmpl.in
@@ -17,7 +17,7 @@
 
 @SET_MAKE@
 
-CC ?= @CC@
+CC = @CC@
 RANLIB = @RANLIB@
 INSTALL = @INSTALL@
 MKDIR_P = @MKDIR_P@