add --static-call-graph option for generating smaller binaries

[JeffBezanson]

This adds a command line option --static-call-graph that builds images where code is only included if it is statically reachable from methods marked using the new function entrypoint. Compile-time errors are given for call sites that are too dynamic to allow trimming the call graph (however there is an unsafe option if you want to try building anyway to see what happens).

The PR has two other components. One is changes to Base that generally allow more code to be compiled in this mode. These changes will either be merged in separate PRs or moved to a separate part of the workflow (where we will build a custom system image for this purpose). The branch is set up this way to make it easy to check out and try the functionality.

The other component is everything in the juliac/ directory, which implements a compiler driver script based on this new option, along with some examples and tests. This will eventually become a package "app" that depends on PackageCompiler and provides a CLI for all of this stuff, so it will not be merged here. To try an example:

cd juliac
../julia juliac.jl --output-exe hello --trim exe_examples/hello_world.jl

When stripped the resulting executable is currently about 900kb on my machine.

Note the script calls this --trim, which will be the official name of this option (following similar functionality in .NET). It is not yet clear if this is identical to the internal --static-call-graph option, or if the latter is an implementation detail of the former.

Also includes a lot of work by @topolarity

[ViralBShah]

➜  juliac git:(jb/gb/static-call-graph) ✗ ../julia juliac.jl --output-exe hello --trim exe_examples/hello_world.jl
ld: warning: ignoring duplicate libraries: '-ljulia'
ld: warning: reexported library with install name '@rpath/libunwind.1.dylib' found at '/Users/viral/julia/usr/lib/libunwind.1.0.dylib' couldn't be matched with any parent library and will be linked directly
run(`cc $(allflags) -o $outname -Wl,$(Base.Linking.WHOLE_ARCHIVE) $img_path -Wl,$(Base.Linking.NO_WHOLE_ARCHIVE) $init_path $(julia_libs)`) = Process(`cc -std=gnu11 -I/Users/viral/julia/usr/include/julia -fPIC -L/Users/viral/julia/usr/lib -L/Users/viral/julia/usr/lib/julia -Wl,-rpath,/Users/viral/julia/usr/lib -ljulia -o hello -Wl,-all_load /var/folders/qj/54cx7lcs2qv9z1b4f_110xb00000gn/T/jl_fPbFYU/img.a -Wl, /var/folders/qj/54cx7lcs2qv9z1b4f_110xb00000gn/T/jl_fPbFYU/init.a -ljulia -ljulia-internal`, ProcessExited(0))

1M binary on Mac M-series:

➜  juliac git:(jb/gb/static-call-graph) ✗ ls -l hello
-rwxr-xr-x  1 viral  staff  1082296 Jul  6 09:57 hello
➜  juliac git:(jb/gb/static-call-graph) ✗ ./hello
Hello, world!
➜  juliac git:(jb/gb/static-call-graph) ✗ otool -L hello
hello:
	@rpath/libjulia.1.12.dylib (compatibility version 1.12.0, current version 1.12.0)
	@rpath/libjulia-internal.dylib (compatibility version 1.12.0, current version 1.12.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1345.100.2)

[timholy]

#55104 gets the lib example working

[MasonProtter]

Let me know if issues should be raised elsewhere, but I ran into a problem where the compiled binaries don't seem to get ARGS. Here's a MWE:

# args.jl
module ArgsDemo

Base.@ccallable function main()::Cint
    ccall(:jl_, Cvoid, (Any,), ARGS)
    return 0
end

end

❯ ~/julia/./julia --startup=no ~/julia/juliac/juliac.jl --output-exe args --trim args.jl
run(`cc $(allflags) -o $outname -Wl,$(Base.Linking.WHOLE_ARCHIVE) $img_path -Wl,$(Base.Linking.NO_WHOLE_ARCHIVE) $init_path $(julia_libs)`) = Process(`cc -std=gnu11 -I/home/masonp/julia/usr/include/julia -fPIC -L/home/masonp/julia/usr/lib -Wl,--export-dynamic -L/home/masonp/julia/usr/lib/julia -Wl,-rpath,/home/masonp/julia/usr/lib -Wl,-rpath,/home/masonp/julia/usr/lib/julia -ljulia -o args -Wl,--whole-archive /tmp/jl_2vsSFl/img.a -Wl,--no-whole-archive /tmp/jl_2vsSFl/init.a -ljulia -ljulia-internal`, ProcessExited(0))

❯ ./args
Array{String, 1}(dims=(0,), mem=Memory{String}(8, 0x5589c120d310)[#<null>, #<null>, #<null>, #<null>, #<null>, #<null>, #<null>, #<null>])

❯ ./args arg1 arg2 agr3
Array{String, 1}(dims=(0,), mem=Memory{String}(8, 0x558aac9f6310)[#<null>, #<null>, #<null>, #<null>, #<null>, #<null>, #<null>, #<null>])