[ltsmaster] Backport LLVM 7 adaptations

[kinke]

Tested with current LLVM branch release_70 on Ubuntu x86_64. Builds fine; default libs too except for an assertion when compiling druntime's ldc.arrayinit (not sure if that's related or simply untested by CI):

ldc2: /home/martin/llvm/include/llvm/Support/Casting.h:255: typename llvm::cast_retty<X, Y*>::ret_type llvm::cast(Y*) [with X = llvm::Function; Y = llvm::Constant; typename llvm::cast_retty<X, Y*>::ret_type = llvm::Function*]: Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
#8 0x00005597f2cb2c5a (bin/ldc2+0x215fc5a)
#9 0x00005597f2cba9b7 llvm::IRBuilderBase::CreateMemCpy(llvm::Value*, unsigned int, llvm::Value*, unsigned int, llvm::Value*, bool, llvm::MDNode*, llvm::MDNode*, llvm::MDNode*, llvm::MDNode*) (bin/ldc2+0x21679b7)
#10 0x00005597f13939b4 DtoMemCpy(llvm::Value*, llvm::Value*, llvm::Value*, unsigned int) /home/martin/ldc/gen/tollvm.cpp:369:0
#11 0x00005597f13ea30d DtoInitClass(TypeClass*, llvm::Value*) /home/martin/ldc/gen/classes.cpp:182:0
#12 0x00005597f13ea45f DtoNewClass(Loc&, TypeClass*, NewExp*) /home/martin/ldc/gen/classes.cpp:112:0

[kinke]

The druntime compile error is due to the changed LLVM memcpy intrinsic; ldc.arrayinit is the only defaultlib module using it. I'll just switch to C memcpy to keep the changes minimal; ldc.intrinsics doesn't fully support LLVM 4.0+ anyway (INTRINSICS_FROM_... only defined for LLVM <= 3.9). As long as it manages to bootstrap LDC and DMD...

[kinke]

Bootstrapping master with the same early LLVM 7 works; master then successfully compiles its default libs. After a little ldmd master fix for LLVM 7, it also passes dmd-testsuite and all but 2 defaultlib tests (std.math, assert(pow(-1.0L, maxOdd) == -1.0L) failing, maybe an LLVM 7 regression; and core.internal.convert, possibly due to slight differences wrt. real literal parsing between master and ltsmaster). So LLVM 7 looking pretty good on Linux x64.

We could use this as 0.17.6; it's ready for LLVM 7 and 2.082. I may get round to adding proper CircleCI incl. automated release+src package generation (we need a prebuilt Linux package for the Travis 0.17.x-host-LDC job for 2.082).

[kinke]

I don't have the energy to look into/fix these ltsmaster CI failures, so just a summary for future reference:

• OSX: 32-bit std.process unittests failing (debug + release). Untested by the single other OSX CI job (Travis), which only tests 64-bit.
• Linux: 2 dmd-testsuite failures (for all 4 configs, i.e. 32/64-bit debug/release).
  1. runnable/sdtor: dmd2/ctfeexpr.c:374: UnionExp copyLiteral(Expression*): Assertion 'ue.exp()->op == TOKarrayliteral' failed. No other existing CI uses an LLVM with enabled assertions, so somewhat understandable that it's only showing now. OSX passes though - there's no OS-specific versioning; only dependency is core.vararg.
  2. runnable/variadic: Not sure why Circle is the only one failing this (there's a Travis job with (vanilla) LLVM 6); I don't think it has anything to do with enabled assertions:

Error: integer constant expression expected instead of <cant>
Error: integer constant expression expected instead of <cant>
Error: integer constant expression expected instead of <cant>
Error: integer constant expression expected instead of <cant>
Error: integer constant expression expected instead of <cant>
runnable/variadic.d(84): Error: template instance variadic.Foo3!(int, int, int) error instantiating

[joakim-noah]

Good to see 0.17.6 released. @redstar, if you plan on keeping the AArch64 buildbot going now that we have Shippable, you may want to update the host ldc 0.17 on there to this release. We'll see a lot more green on there then. :)