precompile: fix deps list for extensions relying on stdlibs

Some packages add extensions to stdlibs, so we should not have
prohibited precompiling those. This broke Compat, which adds an
extension to LinearAlgebra.

Author: vtjnash

base/precompilation.jl

@@ -619,6 +619,7 @@ function _precompilepkgs(pkgs::Union{Vector{String}, Vector{PkgId}},
     for ext_a in keys(ext_to_parent)
         for ext_b in keys(ext_to_parent)
             if triggers[ext_a] ⊋ triggers[ext_b]
+                push!(triggers[ext_a], ext_b)
                 push!(direct_deps[ext_a], ext_b)
             end
         end
@@ -1033,9 +1034,8 @@ function _precompilepkgs(pkgs::Union{Vector{String}, Vector{PkgId}},
                             if interrupted_or_done[]
                                 return
                             end
-                            # for extensions, any extension in our direct dependencies is one we have a right to load
-                            # for packages, we may load any extension (all possible triggers are accounted for above)
-                            loadable_exts = haskey(ext_to_parent, pkg) ? filter((dep)->haskey(ext_to_parent, dep), direct_deps[pkg]) : nothing
+                            # for extensions, any extension that can trigger it needs to be accounted for here (even stdlibs, which are excluded from direct_deps)
+                            loadable_exts = haskey(ext_to_parent, pkg) ? filter((dep)->haskey(ext_to_parent, dep), triggers[pkg]) : nothing
                             if _from_loading && pkg in requested_pkgids
                                 # loading already took the cachefile_lock and printed logmsg for its explicit requests
                                 t = @elapsed ret = begin