Backports for Julia 1.4.0

[KristofferC]

• fix unsigned(::Ptr) and signed(::Ptr) #34941 - fix unsigned(::Ptr) and signed(::Ptr)
• Fix $(PYTHON) paths for native windows executable or cygwin #34984 - Fix $(PYTHON) paths for native windows executable or cygwin

[staticfloat]

@Keno I'm having a tough time figuring out why these windows builds are segfaulting. Logging in and using gdb to get a backtrace, I get the following:

Thread 1 received signal SIGSEGV, Segmentation fault.                                                                                     
0x000000006fd1cc2e in libstdc++-6!_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE9_M_assignERKS4_ ()                                
   from /cygdrive/d/buildbot/worker/package_win64/build/usr/bin/libstdc++-6.dll                                                           
(gdb) bt                                                                                                                                  
#0  0x000000006fd1cc2e in libstdc++-6!_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE9_M_assignERKS4_ ()                            
   from /cygdrive/d/buildbot/worker/package_win64/build/usr/bin/libstdc++-6.dll                                                           
#1  0x00000000668590ff in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::assign (__str=...,             
    this=0xcaf1b0) at /usr/lib/gcc/x86_64-w64-mingw32/9.2.0/include/c++/bits/basic_string.h:1364                                          
#2  std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator= (__str=..., this=0xcaf1b0)                 
    at /usr/lib/gcc/x86_64-w64-mingw32/9.2.0/include/c++/bits/basic_string.h:696                                                          
#3  llvm::MCTargetOptions::operator= (this=0xcaf1a8)                                                                                      
    at /cygdrive/d/buildbot/worker/package_win64/build/usr/include/llvm/MC/MCTargetOptions.h:35                                           
#4  llvm::TargetOptions::operator= (this=0xcaf170)                                                                                        
    at /cygdrive/d/buildbot/worker/package_win64/build/usr/include/llvm/Target/TargetOptions.h:107                                        
#5  llvm::EngineBuilder::setTargetOptions (Opts=..., this=0x8500)                                                                         
    at /cygdrive/d/buildbot/worker/package_win64/build/usr/include/llvm/ExecutionEngine/ExecutionEngine.h:591                             
#6  jl_init_llvm () at /cygdrive/d/buildbot/worker/package_win64/build/src/codegen.cpp:7818                                               
#7  0x0000000066864d67 in jl_init_codegen () at /cygdrive/d/buildbot/worker/package_win64/build/src/codegen.cpp:7905                      
#8  0x00000000668d8fea in _julia_init (rel=(unknown: 1651076188)) at /cygdrive/d/buildbot/worker/package_win64/build/src/init.c:726       
#9  0x00000000668d9815 in julia_init__threading (rel=<optimized out>) at /cygdrive/d/buildbot/worker/package_win64/build/src/task.c:248   
#10 0x0000000000401bcb in wmain (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>)                                        
    at /cygdrive/d/buildbot/worker/package_win64/build/ui/repl.c:211                                                                      
#11 0x00000000004013df in __tmainCRTStartup () at /usr/src/debug/mingw64-x86_64-runtime-7.0.0-1/crt/crtexe.c:334                          
#12 0x000000000040151b in mainCRTStartup () at /usr/src/debug/mingw64-x86_64-runtime-7.0.0-1/crt/crtexe.c:223 

Which seems to point strongly towards cxx11 string ABI issues; however both libjulia.dll and LLVM.dll are using the cxx11-style strings, as far as I can tell. My best guess is that this is triggered by Cygwin moving to GCC 9 by default, and that there may be some issue with the combination of the old LLVM tarballs this branch is using with GCC 9, but I wanted to run this past you first to see if you have any bright ideas.

[Keno]

I agree it looks like a C++11 ABI mismatch. In particular, looks like julia is built with C++11 enabled, but it got a string from somewhere that uses the old ABI.