Explicitly set build modes for tool binaries

[ash2k]

Benefits:

• If built in pure mode tools don't depend on system libc. That means tools are more hermetic. That also should fix (although I don't have evidence) issues on nixos where libc is somewhere else, not in the usual place.
• Tools do not need to be configurable by the --features flag. Currently tools are rebuilt if a flag is toggled.

I've also cleaned it up by extracting shared attributes from two rules.

[jayconrod]

I like the idea of having the tool binaries be pure. I think there's a better way of doing this though.

The simplest thing is probably to just edit _bootstrap_compile and _bootstrap_link so they operate in pure mode. Setting CGO_ENABLED=0 and -linkmode=internal might be good enough.

I'd rather not add any attributes to go_tool_binary which appear to be configurable but are actually ignored (_bootstrap_compile and _bootstrap_link ignore the mode). These will also cause go_rule to attach go_archive_aspect, which probably won't break anything but would be weird.

[ash2k]

It says there is no such flag 🤷‍♀️

usage: compile [options] file.go...
  -%    debug non-static initializers
  -+    compiling runtime
  -B    disable bounds checking
  -C    disable printing of columns in error messages
  -D path
        set relative path for local imports
  -E    debug symbol export
  -I directory
        add directory to import search path
  -K    debug missing line numbers
  -L    show full file names in error messages
  -N    disable optimizations
  -S    print assembly listing
  -V    print version and exit
  -W    debug parse tree after type checking
  -asmhdr file
        write assembly header to file
  -bench file
        append benchmark times to file
  -blockprofile file
        write block profile to file
  -buildid id
        record id as the build id in the export metadata
  -c int
        concurrency during compilation, 1 means no concurrency (default 1)
  -complete
        compiling complete package (no C or assembly)
  -cpuprofile file
        write cpu profile to file
  -d list
        print debug information about items in list; try -d help
  -dolinkobj
        generate linker-specific objects; if false, some invalid code may compile (default true)
  -dwarf
        generate DWARF symbols (default true)
  -dwarflocationlists
        add location lists to DWARF in optimized mode
  -dynlink
        support references to Go symbols defined in other shared libraries
  -e    no limit on number of errors reported
  -f    debug stack frames
  -gendwarfinl int
        generate DWARF inline info records (default 2)
  -goversion string
        required version of the runtime
  -h    halt on error
  -i    debug line number stack
  -importcfg file
        read import configuration from file
  -importmap definition
        add definition of the form source=actual to import map
  -installsuffix suffix
        set pkg directory suffix
  -j    debug runtime-initialized variables
  -l    disable inlining
  -linkobj file
        write linker-specific object to file
  -live
        debug liveness analysis
  -m    print optimization decisions
  -memprofile file
        write memory profile to file
  -memprofilerate rate
        set runtime.MemProfileRate to rate
  -msan
        build code compatible with C/C++ memory sanitizer
  -mutexprofile file
        write mutex profile to file
  -nolocalimports
        reject local (relative) imports
  -o file
        write output to file
  -p path
        set expected package import path
  -pack
        write package file instead of object file
  -r    debug generated wrappers
  -race
        enable race detector
  -s    warn about composite literals that can be simplified
  -shared
        generate code that can be linked into a shared library
  -std
        compiling standard library
  -traceprofile file
        write an execution trace to file
  -trimpath prefix
        remove prefix from recorded source file paths
  -u    reject unsafe code
  -v    increase debug verbosity
  -w    debug type checking
  -wb
        enable write barrier (default true)
flag provided but not defined: -linkmode

[jayconrod]

Oops, -linkmode internal is only needed for go tool link.

And actually, never mind about CGO_ENABLED=0. That will have no effect with these commands.