[cilkplus] misc cleanups for <#pragma simd> implementation

[Aldy Hernandez <aldyh at redhat dot com>]

Hi Balaji.

This is a patch against, the [cilkplus] branch (not the [cilkplus-merge] 
branch).  I have taken the liberty to start cleaning up the <#pragma 
simd> stuff on your development branch, while the array notation 
patchset is being reviewed by Joseph.

Herein lies a potpourri of fixes, refactoring, and cleanups.  They 
should all be pretty obvious.

There are two main functional changes:

1. I removed setting of flag_vectorize in the front-end.  This is 
certainly not going to fly.  Instead, I am issuing an error when 
<#pragma simd> is used without -ftree-vectorize.  For testing I have 
added the appropriate flag when tests are running at lower optimization 
levels.

2. I noticed some of the errors wrt <#pragma simd> were pointing to the 
wrong place.  I have saved the location_t of the original #pragma and 
saved this in the global pragma simd table.  This makes errors more 
meaningful.

I have added various FIXME notes throughout for things I plan to tackle 
next.  If you prefer me not adding such notes, I can remove them, but 
rest assured, I'll work on them shortly.

I have renamed the {compile,errors,execute}.exp files to something less 
ambiguous.  As explained before, this makes it easier to test individual 
components, ala "make check-gcc RUNTESTFLAGS=foo.exp".

There are no regressions with this patch, but I noticed all the tests in 
gcc.dg/cilk-plus/pragma_simd_tests/execute/ were failing before my patch:

	/usr/bin/ld: cannot find -lcilkrts
	collect2: error: ld returned 1 exit status
	compiler exited with status 1

I don't see a -L in the command line, but I didn't bother to look into 
it.  It was broken before ;-).

Finally, building the toolchain seems to automagically regenerate the 
following files:

	#       modified:   ../../../libcilkrts/Makefile.in
	#       modified:   ../../../libcilkrts/aclocal.m4
	#       modified:   ../../../libcilkrts/configure

Is this on purpose?  Should I check in the modified files?  FWIW, I am 
*not* including these modified files into this patch.

Oh, one more thing... assuming you are keeping a merged set of ChangeLog 
entries for eventual merging, I am only including changelog entries for 
new code I am touching.  I assume, there are already entries for code 
you have already touched.

OK to commit to cilkplus branch?

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