Emphasize how `isimmutable` works for types.

Ref: #8760
fix #7982 -- add backtrace information for win32
windows: add backtrace/unwind info for win32 with MCJIT
windows: actually fix #8413 and maybe fix #7982 also
windows: wip: attempt enabling debuginfo/backtraces/error-catching for win64 mcjit
windows: wip: correct data pointers in win64 debug info commit
reduce memory usage on win32 from unnecessary unwind info
unbreak win64 backtraces with llvm JIT
reduce memory usage of win64 backtrace info
add stackwalk information for win32
unbreak windows build
windows: avoid infinite recursion in _exception_handler
Merge pull request #8928 from ivarne/isimmutable

Emphasize how `isimmutable` works for types.
make curl flags more robust in msys_build.sh

use https://status.julialang.org

set MARCH on appveyor
 implement stackwalk information for win32
remove unused code from win32 backtrace support wip
restore backtrace test

since this PR fixes it
re-enable sys.dll on win32
Merge pull request #9190 from JuliaLang/jn/win32_backtraces

improve/fix windows backtraces and win64 memory over-consumption issue
Forcefully add files in `Pkg.generate`

Makes the generation more robust and avoids potential clashes with any
global `.gitignore`.