[gomp4.1] coerce libgomp to build with C++

[Aldy Hernandez <aldyh at redhat dot com>]

Ughh... what was supposed to be a short hack turned out to be 2 days of 
pure torture.

So...I'm implementing task priorities as per the 4.1 standard, and 
decided to use a priority queue.  Since we already have splay trees in 
libgomp, I figured these priority queues could be built on top of them. 
 However, our libgomp splay tree adaptation is not exactly generic 
enough, so I started rewriting it to use C++ templates.

I quickly found out that libgomp is built with C, so I said to myself... 
"Self, how bad can it be to convert libgomp to C++?".  Very.

I've pretty much renounced the splay tree in C++ idea, but only because 
I don't want to iron out the remaining automake/configury magic, not to 
mention possible ABI issues I've yet to uncover.  However, throwing 2 
days' worth of work away would be silly, so how about we pass 
-Wc++-compat and avoid further C/C++ divergence?

I have tested this patch as is, as well as with:

	AM_CFLAGS = $(XCFLAGS) -x c++

Using the C++ compiler compiles, but does not link:

/usr/bin/ld: .libs/loop.o: relocation R_X86_64_PC32 against undefined 
symbol `gomp_ialias_GOMP_parallel_end' can not be used when making a 
shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Bad value

I really must get back to task priorities, so I'm not going to pursue 
C++ linking any further.  However, the attached patch should get us 95% 
of the way there, and we can keep it going forward.

I could provide a trunk version of this, but considering gomp4.1 will 
get merged (*crosses fingers*), no sense in doing the work twice.

Most everything is obvious.  The things that are not, or I'm unsure 
about, I have documented throughout.

OK for gomp4.1 branch?

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