Some more compiler refactors (#1165)

Extract the compile method basics into a separate module, add some
comments.
Hopefully this should make it easier to understand the code.

doc/reference/dev/bootstrap.md

@@ -181,7 +181,7 @@ $ mkdir -p bootstrap/gerbil
 $ cp gerbil/builtin.ssxi.ss bootstrap/gerbil
 
 # compile the bootstrap with the current installed compiler
-$ gxc -O -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
+$ gxc -O -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,method,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
 ```
 
 ### Recursively Recompiling the bootstrap
@@ -195,15 +195,15 @@ bootstrap recompilation.
 ```
 $ cd src
 $ rm -rf bootstrap/*
-$ gxc -no-ssxi -O -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
+$ gxc -no-ssxi -O -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,method,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
 ```
 
 If you have made changes in the compiler optimizer meta and the extant
 compiler does not accept your code (or generates broken code), you may
 want to try without optimizations:
 
 ```
-$ gxc -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
+$ gxc -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,method,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
 ```
 
 Otherwise, you are likely violating some of the bootstrap strictures; see below.
@@ -231,7 +231,7 @@ $ cd src
 $ rm -rf bootstrap/*
 $ mkdir -p bootstrap/gerbil
 $ cp gerbil/builtin.ssxi.ss bootstrap/gerbil
-$ ../build.sh env gxc -O -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
+$ ../build.sh env gxc -O -d bootstrap -s -S gerbil/core/{runtime,expander,sugar,mop,macro-object,match,more-sugar,more-syntax-sugar,module-sugar}.ss gerbil/core.ss gerbil/runtime/{gambit,util,table,control,system,c3,mop,error,interface,hash,thread,syntax,eval,repl,loader,init}.ss gerbil/runtime.ss gerbil/expander/{common,stx,core,top,module,compile,root,stxcase}.ss gerbil/expander.ss gerbil/compiler/{base,method,compile,optimize-base,optimize-xform,optimize-top,optimize-spec,optimize-ann,optimize-call,optimize,driver,ssxi}.ss gerbil/compiler.ss gerbil/gambit.ss
 ```
 
 And you have a brand new recursive bootstrap you can use. From here