add jl_get_cpu_name function to libjulia

thin ccall'able wrapper around llvm::sys::getHostCPUName
Modify jl_get_cpu_name to use jl_pchar_to_string,

add Sys.cpu_name
Move cpu_name into init_sysinfo()
Include file information in emitted debug info
Header improvements to conform to MELPA's standards.
In backtraces, the scope may now not be the DISubprogram
All julia functions and variables should be prefixed.

Elisp doesn't have namespaces, so this is the best way to prevent name
clashes between packages. However, it's possible that users may have
Emacs configuration that calls the functions with their old names, so
I've set up aliases.
Merge pull request #7979 from Wilfred/fixes_for_melpa

Fixes for MELPA
Merge pull request #6660 from JuliaLang/kf/filediinfo

Include file information in emitted debug info
Two small llvmcall fixes imported from cxx branch
Merge pull request #7552 from tkelman/getcpuname

RFC: add jl_get_cpu_name function to libjulia