Update openlibm to master and install it properly

This is more standard and it's required for a future
fix making openspecfun no longer include headers from the
openlibm source directory.
Fix bug in more-than-6D SubArray indexing
Yield error on to_index with non-Real argument

Fixes #6017
Allow Real when scalar-ndexing on 7th+ dimension
Fix typo in repackage_system_suitesparse4.make
Missing parentheses on JULIA_VERSION

leads to installing to `julia-ULIA_VERSION` when `NO_GIT = 1`
Fix install and win-extras for Cygwin cross

- call cygpath_w on julia executable for stringpatch
- don't try to copy p7zip bin and lib into dist-extras on Cygwin
- chmod a+x on both 7z.exe and 7z.dll, before first running 7z.exe
Fix #6036
Merge pull request #6043 from tkelman/patch-2

Missing parentheses on JULIA_VERSION
Merge pull request #6038 from Manticore/patch-1

Fix typo in repackage_system_suitesparse4.make
correct rl_startup_hook type while USE_SYSTEM_READLINE=1
fix #6031, `@m(x)[3]` syntax
Merge branch 'master' of github.com:JuliaLang/julia
mitigate #6016

at least avoid ever printing the nonsensical "alue" string
Merge pull request #6001 from nalimilan/openlibm

Update openlibm to master and install it properly
Merge pull request #6046 from KDr2/kd/sys_rl

correct rl_startup_hook type while USE_SYSTEM_READLINE=1
New norm(Matrix) behavior to NEWS
Merge pull request #6037 from JuliaLang/cb/index

some indexing tweaks
fix #6050
Merge pull request #6045 from tkelman/patch-3

Fix install and win-extras for Cygwin cross