Fix #698 — ICE with minimal D runtime and basic `extern(C) int main()` function
Work around for LLVM bug 21016.

LLVMX86Utils is missing from target library list for target X86.
Affects only MSVC build.
Merge pull request #700 from AlexeyProkhin/issue698

Fix #698 — ICE with minimal D runtime and basic `extern(C) int main()` function
Do not use doubledouble on PPC32/64.

doubledouble has only incomplete support in Phobos.
Also includes a druntime fix (cherry-picked from master)
More support for PPC64le target.
Fix threadasm.S for PPC64le
fix C2883 in MSVC build
remove all the "tmp" IR names
fix configuration for llvm builds with assertions
attempt to make portable installation possible