Assumes G++ binary is `g++-10`

[owainkenwayucl]

Currently build.jl assumes that the C++ compiler is g++-10 by default if CXX is not set. This of course breaks on systems which don't have a g++-10, e.g. on Mandelbrot.

IPUToolkit.jl/deps/build.jl

Line 37 in 60b3fad

cxx = get(ENV, "CXX", "g++-10")

  [3f19e933] + p7zip_jll v17.4.0+0
    Building IPUToolkit → `~/.julia/scratchspaces/44cfe95a-1eb2-52ea-b672-e2afdf69b78f/096b5ec0dcdf1f621bdc8196869fb21ee736377b/build.log`
ERROR: Error building `IPUToolkit`: 
ERROR: LoadError: IOError: could not spawn `g++-10 -x c++ -E -Wp,-v - -fsyntax-only`: no such file or directory (ENOENT)
Stacktrace:
  [1] _spawn_primitive(file::String, cmd::Cmd, stdio::Vector{Union{RawFD, IO}})
    @ Base ./process.jl:128
  [2] (::Base.var"#784#785"{Cmd})(stdios::Vector{Union{RawFD, IO}})
    @ Base ./process.jl:139 [inlined]
  [3] setup_stdios(f::Base.var"#784#785"{Cmd}, stdios::Vector{Union{RawFD, IO}})
    @ Base ./process.jl:223
  [4] _spawn(cmd::Cmd, stdios::Vector{Union{RawFD, IO}})
    @ Base ./process.jl:138 [inlined]
  [5] _spawn(::Base.CmdRedirect, ::Vector{Union{RawFD, IO}}) (repeats 2 times)
    @ Base ./process.jl:166
  [6] open(cmds::Base.CmdRedirect, stdio::Base.DevNull; write::Bool, read::Bool)
    @ Base ./process.jl:393
  [7] open(cmds::Base.AbstractCmd, stdio::Union{RawFD, Base.FileRedirect, IO})
    @ Base ./process.jl:383 [inlined]
  [8] open(cmds::Base.CmdRedirect, mode::String, stdio::Base.DevNull)
    @ Base ./process.jl:364
  [9] read(cmd::Base.CmdRedirect)
    @ Base ./process.jl:447
 [10] read
    @ Base ./process.jl:458 [inlined]
 [11] readchomp(x::Base.CmdRedirect)
    @ Base ./io.jl:974 [inlined]
 [12] get_system_includes()
    @ Main ~/.julia/packages/IPUToolkit/xzppr/deps/build.jl:39
 [13] gen_bindings(headers::Vector{String}, blacklist::Vector{String})
    @ Main ~/.julia/packages/IPUToolkit/xzppr/deps/build.jl:589
 [14] build_bindings(; path::String, generate_bindings::Bool, compile::Bool)
    @ Main ~/.julia/packages/IPUToolkit/xzppr/deps/build.jl:619
 [15] build_bindings()
    @ Main ~/.julia/packages/IPUToolkit/xzppr/deps/build.jl:617
 [16] top-level scope
    @ ~/.julia/packages/IPUToolkit/xzppr/deps/build.jl:663
 [17] include(fname::String)
    @ Base.MainInclude ./client.jl:489
 [18] top-level scope
    @ none:5
in expression starting at /home/uccaoke/.julia/packages/IPUToolkit/xzppr/deps/build.jl:663

Obviously this can be worked around by setting CXX or by having sym-linked g++-10 in path but it should probably default to a more common thing e.g. just g++.