[WIP] test enabling i128 lowering for emscripten

[est31]

Maybe this fixes the issues emscripten has with i128. Maybe not.

DO NOT MERGE

[est31]

I see the following failures:

run-pass/float-int-invalid-const-cast.rs

[01:35:06]   = note: Unsupported:   call void @_ZN28float_int_invalid_const_cast5force17haaefff15b0074e85E(i128 0)
[01:35:06]           LLVM ERROR: Instruction not yet supported for integer types larger than 64 bits
[01:35:06]           Traceback (most recent call last):
[01:35:06]             File "/emsdk-portable/emscripten/1.37.13//emcc", line 13, in <module>
[01:35:06]               emcc.run()
[01:35:06]             File "/emsdk-portable/emscripten/1.37.13/emcc.py", line 1526, in run
[01:35:06]               final = shared.Building.emscripten(final, append_ext=False, extra_args=extra_args)

run-pass/i128.rs

[01:35:06]   = note: Unsupported:   %699 = call { i128, i1 } @llvm.smul.with.overflow.i128(i128 11259375, i128 11259375)
[01:35:06]           LLVM ERROR: Instruction not yet supported for integer types larger than 64 bits

run-pass/intrinsics-integer.rs

[01:35:06]   = note: Unsupported:   %2311 = call i128 @llvm.ctpop.i128(i128 0)
[01:35:06]           LLVM ERROR: Instruction not yet supported for integer types larger than 64 bits

run-pass/saturating-float-casts.rs

[01:35:06]   = note: Unsupported:   %20610 = fptosi float %20609 to i128
[01:35:06]           LLVM ERROR: Instruction not yet supported for integer types larger than 64 bits

So every test I enabled failed. It tested the asmjs-unknown-emscripten target.

[est31]

Unsupported: call void @_ZN28float_int_invalid_const_cast5force17haaefff15b0074e85E(i128 0)
LLVM ERROR: Instruction not yet supported for integer types larger than 64 bits

hmmm this is something else than lowering that fails.

[scottmcm]

Not even being able to pass/return i128 was what blocked me last time:

rust/src/test/mir-opt/lower_128bit_debug_test.rs

Lines 11 to 14 in 15e8c5d

	// asmjs can't even pass i128 as arguments or return values, so ignore it.
	// this will hopefully be fixed by the LLVM 5 upgrade (#43370)
	// ignore-asmjs
	// ignore-emscripten

[est31]

Guess I'm closing this then.