Recommit r171461 which was incorrectly reverted. Mark DIV/IDIV instructions hasSideEffects=1 because they can trap when dividing by 0. This is needed to keep early if conversion from moving them across basic blocks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171608 91177308-0d34-0410-b5e6-96231b3b80d8
Emit DW_TAG_formal_parameter for unnamed parameters.

This change essentially reverts r87069 which came without a test case. It
causes no regressions in the GDB 7.5 test suite & fixes 25 xfails (commit
to the test suite to follow). If anyone can present a test case that
demonstrates why this check is necessary I'd be happy to account for it in one
way or another.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171609 91177308-0d34-0410-b5e6-96231b3b80d8
IR/Attributes: Provide EmptyKey and TombstoneKey in part of enum, as workaround for gcc-4.4 take #2.

I will investigate, later, what was wrong. I am too tired for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171611 91177308-0d34-0410-b5e6-96231b3b80d8