Migrating mips/mips64 to clang/llvm [update 3, with real bugs]

[Sean Bruno]

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tl;dr: linking libc fails at the moment if I wave my hands a lot and
patch out of dim's clang36 branch

Quite a bit of progress today (mainly thanks to Ed mentoring and
letting me cut-n-paste some ASM code).  We're not linking together
libc correctly.

So we've got a few things going on:

.cprestore unsupported http://llvm.org/bugs/show_bug.cgi?id=20967
 -- even with this patch, I need to comment out the warning about PIC.
 -- Ed confirms that .cprestore is a no-op on mips if PIC isn't enabled.
 -- This leads us to the following 4 patches that are under review.
   - http://reviews.llvm.org/D6267
   - http://reviews.llvm.org/D5626
   - http://reviews.llvm.org/D5601
   - http://reviews.llvm.org/D6231

With those in place, and the support for our target triple in clang, I
can progress further.  We then run into unsupported GAS macros, which
are the subject of http://llvm.org/bugs/show_bug.cgi?id=21474

Currently, libc moves to the linking stage and fails:

building shared library libc.so.7
/var/tmp/mips.mips/home/sbruno/bsd/clang360-import/tmp/usr/bin/ld:
/var/tmp/mips.mips/home/sbruno/bsd/clang360-import/tmp/usr/lib/crtbeginS.o:
CALL16 reloc at 0x8 not against global symbol
/var/tmp/mips.mips/home/sbruno/bsd/clang360-import/tmp/usr/lib/crtbeginS.o:
could not read symbols: Bad value
cc: error: linker command failed with exit code 1 (use -v to see
invocation)
*** Error code 1


sean

Unified diff of my current tree based on the projects/clang360 import
branch.  https://people.freebsd.org/~sbruno/clang_mips.diff
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