This assertion is failing for me at head with this reduced repro (using a debug build of clang):

$ cat repro.cc 
template <typename>
class b {
  __attribute__((target("avx"))) void c();
};
class B {
 public:
  __attribute__((target("avx"))) __attribute__((always_inline)) B();
};
template <typename d>
void b<d>::c() {
  B a;
}
template class b<int>;

$ clang++ -c repro.cc
clang++: llvm-project/clang/include/clang/AST/GlobalDecl.h:45: void clang::GlobalDecl::Init(const clang::Decl *): Assertion `!isa<CXXConstructorDecl>(D) && "Use other ctor with ctor decls!"' failed.
Stack dump:
0.      Program arguments: clang++ -c repro.cc
1.      repro.cc:13:22: current parser token ';'
2.      repro.cc:3:39: instantiating function definition 'b<int>::c'
3.      repro.cc:3:39: LLVM IR generation of declaration 'b<int>::c'
4.      repro.cc:3:39: Generating code for declaration 'b<int>::c'
 #0 0x0000000007f89b17 llvm::sys::PrintStackTrace(llvm::raw_ostream&) llvm-project/llvm/lib/Support/Unix/Signals.inc:564:11
... <irrelevant stack unwinding> ...
#11 0x00000000082d580f clang::GlobalDecl::Init(clang::Decl const*) llvm-project/clang/include/clang/AST/GlobalDecl.h:46:5
#12 0x00000000082ded19 clang::GlobalDecl::GlobalDecl(clang::FunctionDecl const*, unsigned int) llvm-project/clang/include/clang/AST/GlobalDecl.h:57:3
#13 0x0000000008615705 clang::CodeGen::CodeGenFunction::checkTargetFeatures(clang::SourceLocation, clang::FunctionDecl const*) llvm-project/clang/lib/CodeGen/CodeGenFunction.cpp:2351:22
#14 0x000000000842a99d clang::CodeGen::CodeGenFunction::EmitCall(clang::CodeGen::CGFunctionInfo const&, clang::CodeGen::CGCallee const&, clang::CodeGen::ReturnValueSlot, clang::CodeGen::CallArgList const&, llvm::CallBase**, clang::SourceLocation) llvm-project/clang/lib/CodeGen/CGCall.cpp:3977:41
#15 0x00000000085e0d53 clang::CodeGen::CodeGenFunction::EmitCall(clang::CodeGen::CGFunctionInfo const&, clang::CodeGen::CGCallee const&, clang::CodeGen::ReturnValueSlot, clang::CodeGen::CallArgList const&, llvm::CallBase**) llvm-project/clang/lib/CodeGen/CodeGenFunction.h:3621:12
#16 0x000000000862c70b clang::CodeGen::CodeGenFunction::EmitCXXConstructorCall(clang::CXXConstructorDecl const*, clang::CXXCtorType, bool, bool, clang::CodeGen::Address, clang::CodeGen::CallArgList&, clang::CodeGen::AggValueSlot::Overlap_t, clang::SourceLocation, bool) llvm-project/clang/lib/CodeGen/CGClass.cpp:2177:3
#17 0x000000000862be8e clang::CodeGen::CodeGenFunction::EmitCXXConstructorCall(clang::CXXConstructorDecl const*, clang::CXXCtorType, bool, bool, clang::CodeGen::AggValueSlot, clang::CXXConstructExpr const*) llvm-project/clang/lib/CodeGen/CGClass.cpp:2094:1
#18 0x00000000087c2e2e clang::CodeGen::CodeGenFunction::EmitCXXConstructExpr(clang::CXXConstructExpr const*, clang::CodeGen::AggValueSlot) llvm-project/clang/lib/CodeGen/CGExprCXX.cpp:651:1
#19 0x000000000877dc7e (anonymous namespace)::AggExprEmitter::VisitCXXConstructExpr(clang::CXXConstructExpr const*) llvm-project/clang/lib/CodeGen/CGExprAgg.cpp:1269:1
#20 0x0000000008779b90 clang::StmtVisitorBase<std::add_pointer, (anonymous namespace)::AggExprEmitter, void>::Visit(clang::Stmt*) llvm-build/dev/tools/clang/include/clang/AST/StmtNodes.inc:679:1
#21 0x00000000087777ab (anonymous namespace)::AggExprEmitter::Visit(clang::Expr*) llvm-project/clang/lib/CodeGen/CGExprAgg.cpp:107:3
#22 0x00000000087773b4 clang::CodeGen::CodeGenFunction::EmitAggExpr(clang::Expr const*, clang::CodeGen::AggValueSlot) llvm-project/clang/lib/CodeGen/CGExprAgg.cpp:1849:1
...