[Hexagon] Adding double word add/min/minu/max/maxu instructions and tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224153 91177308-0d34-0410-b5e6-96231b3b80d8
Clean up static analyzer warnings.

Clang's static analyzer found several potential cases of undefined
behavior, use of un-initialized values, and potentially null pointer
dereferences in tablegen, Support, MC, and ADT. This cleans them up
with specific assertions on the assumptions of the code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224154 91177308-0d34-0410-b5e6-96231b3b80d8
utils: update vim syntax highlighting for LLVM IR

Add missing externally_initialized keyword from SVN r174340.  Also reflow the
text.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224155 91177308-0d34-0410-b5e6-96231b3b80d8