[Cygwin] Fix global variable dll import (#121439)

This PR is necessary for cygwin target of Rust.

References:
*
rust-lang@86657cc
*
Berrysoft@a807e9f

Author: Berrysoft

llvm/lib/Target/TargetMachine.cpp

@@ -204,7 +204,7 @@ bool TargetMachine::shouldAssumeDSOLocal(const GlobalValue *GV) const {
     // don't assume the variables to be DSO local unless we actually know
     // that for sure. This only has to be done for variables; for functions
     // the linker can insert thunks for calling functions from another DLL.
-    if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
+    if (TT.isOSCygMing() && GV->isDeclarationForLinker() &&
         isa<GlobalVariable>(GV))
       return false;
 

llvm/test/CodeGen/X86/mingw-refptr.ll

@@ -1,4 +1,5 @@
 ; RUN: llc < %s -mtriple=x86_64-w64-mingw32 | FileCheck %s -check-prefix=CHECK-X64
+; RUN: llc < %s -mtriple=x86_64-pc-cygwin | FileCheck %s -check-prefix=CHECK-X64
 ; RUN: llc < %s -mtriple=i686-w64-mingw32 | FileCheck %s -check-prefix=CHECK-X86
 ; RUN: llc < %s -mtriple=i686-w64-mingw32-none-elf | FileCheck %s -check-prefix=CHECK-X86-ELF