Hide IRShow include from Revise

Revise in theory wants to re-evaluate this include, but it fails at doing so,
because the include call no longer works after bootstrap. It happens
to work right now on master, because the lowering of `Compiler.include`
happens to hide the include call from Revise, but that's a Revise bug
I'm about to fix. Address this by moving the include call into the
package and using an absolute include if necessary.

Compiler/src/Compiler.jl

@@ -182,11 +182,20 @@ include("reflection_interface.jl")
 include("opaque_closure.jl")
 
 module IRShow end
+function load_irshow!()
+    if isdefined(Base, :end_base_include)
+        # This code path is exclusively for Revise, which may want to re-run this
+        # after bootstrap.
+        include(IRShow, Base.joinpath(Base.dirname(@__FILE__), "ssair/show.jl"))
+    else
+        include(IRShow, "ssair/show.jl")
+    end
+end
 if !isdefined(Base, :end_base_include)
     # During bootstrap, skip including this file and defer it to base/show.jl to include later
 else
     # When this module is loaded as the standard library, include this file as usual
-    include(IRShow, "ssair/show.jl")
+    load_irshow!()
 end
 
 end # baremodule Compiler

base/show.jl

@@ -2821,7 +2821,7 @@ function show(io::IO, vm::Core.TypeofVararg)
     end
 end
 
-Compiler.include(Compiler.IRShow, "ssair/show.jl") # define `show` for the compiler types
+Compiler.load_irshow!()
 const IRShow = Compiler.IRShow # an alias for compatibility
 
 function show(io::IO, src::CodeInfo; debuginfo::Symbol=:source)