Reporting here also:
---
[/usr/lib/gcc/x86_64-linux-gnu/6/include/d/std/range/package.d:795:6] chain (ByCodeUnitImpl _param_0, OnlyResult!(char, 1LU) _param_1, ByCodeUnitImpl _param_2)
../source/backends/archlinux/alpkg.d:28:8: internal compiler error: Aborted
 import backends.interfaces;
        ^
0xad169f crash_signal
 ../../src/gcc/toplev.c:333
0x6af86e Mangler::mangleFunc(FuncDeclaration*, bool)
 ../../src/gcc/d/dfrontend/mangle.c:384
0x6ae518 mangleExact(FuncDeclaration*)
 ../../src/gcc/d/dfrontend/mangle.c:877
0x71ea95 FuncDeclaration::toSymbol()
 ../../src/gcc/d/d-decls.cc:304
0x71feeb d_decl_context(Dsymbol*)
 ../../src/gcc/d/d-codegen.cc:313
0x74dc90 TypeVisitor::visit(TypeStruct*)
 ../../src/gcc/d/types.cc:275
0x74d95d build_ctype(Type*)
 ../../src/gcc/d/types.cc:503
0x71f432 AggregateDeclaration::toInitializer()
 ../../src/gcc/d/d-decls.cc:720
0x65ac7c CallExp::semantic(Scope*)
 ../../src/gcc/d/dfrontend/expression.c:8462
0x6f4e4f ReturnStatement::semantic(Scope*)
 ../../src/gcc/d/dfrontend/statement.c:3900
0x6f25d1 CompoundStatement::semantic(Scope*)
 ../../src/gcc/d/dfrontend/statement.c:1165
0x677b74 FuncDeclaration::semantic3(Scope*)
 ../../src/gcc/d/dfrontend/func.c:1559
0x6ffc83 TemplateInstance::semantic3(Scope*)
 ../../src/gcc/d/dfrontend/template.c:7618
0x7063b2 TemplateInstance::trySemantic3(Scope*)
 ../../src/gcc/d/dfrontend/template.c:5811
0x70c8ce TemplateInstance::semantic(Scope*, Array<Expression*>*)
 ../../src/gcc/d/dfrontend/template.c:6213
0x70cd09 functionResolve(Match*, Dsymbol*, Loc, Scope*, Array<RootObject*>*, Type*, Array<Expression*>*)
 ../../src/gcc/d/dfrontend/template.c:2578
0x671329 resolveFuncCall(Loc, Scope*, Dsymbol*, Array<RootObject*>*, Type*, Array<Expression*>*, int)
 ../../src/gcc/d/dfrontend/func.c:3320
0x658512 CallExp::semantic(Scope*)
 ../../src/gcc/d/dfrontend/expression.c:8853
0x6f4e4f ReturnStatement::semantic(Scope*)
 ../../src/gcc/d/dfrontend/statement.c:3900
0x6f25d1 CompoundStatement::semantic(Scope*)
 ../../src/gcc/d/dfrontend/statement.c:1165
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-6/README.Bugs> for instructions.
---

Backtrace shows that we are in semantic analysis stage, when a *sudden* call into the backend occurs.