[PATCH] Add a makefile check for misbehaving -Wcomment

[Filipe Cabecinhas]

Eric, is that huge added block a problem? I'm not sure why autoconf changed what it had.

My env is:

```
$ ./autoconf/AutoRegen.sh

### NOTE: ############################################################
### If you get *any* warnings from autoconf below you MUST fix the
### scripts in the m4 directory because there are future forward
### compatibility or platform support issues at risk. Please do NOT
### commit any configure script that was generated with warnings
### present. You should get just three 'Regenerating..' lines.
######################################################################

Regenerating aclocal.m4 with aclocal 1.9.6
Regenerating configure with autoconf 2.60
Regenerating config.h.in with autoheader 2.60
```

================
Comment at: configure:19786
@@ -19785,3 +19853,2 @@
 LIBOBJS!$LIBOBJS$ac_delim
-LTLIBOBJS!$LTLIBOBJS$ac_delim
 _ACEOF
----------------
I'm not sure why this changed to the huge block @ line 19892

http://reviews.llvm.org/D5946